It can be hard to recommend a long-running series. It's a huge money sink, and you buy hoping that you'll get a satisfactory ending but not actually knowing this (mainly as the series is still running in Japan). One of my favoite current manga, Mahou Sensei Negima, also has two other big problems in recommending it to new readers.
First, the adaptation is all over the map. It's changed translators and adaptors at least 3 times, and each group has a new approach. The early volumes got character names completely wrong (Shen Rin? Try Lingshen Chao.), and its adaptation by noted comics writer Peter David was... loose, to be polite.
Second, I'll be honest. The first three volumes aren't very good. They suffer from an overuse of Akamatsu's traditional 'fan service' and 'comedic violence' that he'd already done to death in his bestselling predecessor, Love Hina. Now, neither of those go away entirely, but in future volumes they either get toned down or spaced apart better. And the 'tsundere' characters get much better defined here as being more than a hair-trigger temper and an angry punch.
And then there's the basic premise. By now most casual readers know the story about Akamatsu slowly changing his manga from being a harem manga with magic to being a fighting manga with magic, but the romance still exists. This despite the hero being ten years old, and most of the girls being fourteen. Japan has a casual relationship with age in its anime and manga, and even though most of the romance in Negima is 'innocent', limited to confessions of love and admiration or kisses to get magical abilities, it can still make a reader uncomfortable.
That said, I think Negima is, especially lately, a fantastic example of a shonen manga. It's hitting exactly the right beats, balancing well between epic fight sequences, gripping plot revelations, touching character development, and yes, the occasional naked girls bath scenes. This posts lists what I consider to be 10 of the defining moments in the 27 volumes of Negima released to date by Del Rey. And trust me, it took a lot of narrowing down. They're listed in order from earliest to most recent. And yes, there are some spoilers here, but I will try to gush about the moment while not revealing TOO much.
1) Nodoka's Confession (Volume 4). So often in shonen harem manga, especially ones involving a pile of girls and one guy going nowhere for several volumes, we get the classic aborted confession. The girl tries to indicate that she likes the guy, but is either too shy, or he misunderstands, or some sort of chaos prevents them from doing anything. So she backs off, resolving to try again later on. Nowhere is this more apparent than in Love Hina, Akamatsu's prior manga. And Nodoka was having a lot of trouble separating herself from Shinobu, the character in Love Hina she most resembles. So it was a big surprise when, after a chapter of waffling, she buckles down and admits that she's fallen in love with Negi. This ends up being the defining moment of her character. She's shy, and prone to panic and second-guessing, but when the pressure is on, she's the most courageous of the entire cast. It also sets up later moments when her courage goes beyond love and into risking her life - literally - for her friends.
2) Setsuna's Reveal and subsequent aftermath (Volume 6). Setsuna was introduced in Volume 4 as a 'shadow' bodyguard for Konoka, the term being in quotes as it's Setsuna herself who lurks in the shadows, humiliated by her past failure to save Konoka (when they were both small children) and determined that she can only protect her by never getting close to her again. What's more, she's covering up a hidden heritage, one which gives her even more self-loathing problems. So when it becomes clear that Konoka will be sacrificed unless something is done, Setsuna reveals her true, ugly form... a pair of huge, fluffy white angel wings. (Technically she's apparently some sort of albino half-crow demon, but they look like big, fluffy angel wings). After briefly boggling and noting how pretty the wings look, Asuna notes that Setsuna, who knows Konoka better than anyone, should know that she'd never care about something like that. Sure enough, once Setsuna rescues Konoka from the bad guys, Konoka's first thought is that she looks beautiful. Not only does this play up having more confidence in yourself (a constant theme of Negima), but it starts the KonoSetsu yuri pairing love. The manga has no ACTUAL romantic couples, but if it did, these two would be one. They're just adorable together.
3) Evangeline to the rescue (Volume 6). Let's face it, when you're an undead vampire mage trapped in the body of a small girl, it's hard to get respect. This applies both to people in story and out. And the reader didn't think much of Evangeline when she was defeated fairly easily by Negi and Asuna in Volume 3. So, since Akamatsu already planned to have Negi taught more magic by Evangeline as a mentor figure (albeit a semi-evil one), how to how that she's actually incredibly super-powerful when she's actually concentrating and taking her opponent seriously? Well, one way would be to have her show up in the middle of the final fight, casually have her robot familiar trap the demonic monster that's towering over the whole area in a magic barrier, and then destroying it with one casual spell. Oh, and after getting her entire body run through with a giant stone spike by Fate, who had been manhandling Negi and Asuna earlier, she casually re-forms her body and slams Fate around. Then he RUNS AWAY. All this punctuated with maniacal laughter. If you're going to introduce a badass mentor, show why they're badass. Oh yes, and one of the more pathetic evil minions gets owned by Eva's crazy puppet. No, literally a puppet. With strings and everything.
4) Kaede vs. 'Ku:Nel Sanders' (Volume 13). Despite all the lip service Akamatsu gave to 'All of the 31 girls in the class will be important to the story', Negima like every other series with huge casts has its star players and its supporting characters. Kaede, the huge ninja girl, sort of sits between the two poles. She's at her best here, in the midst of a giant tournament arc, going up against a new character who has shown up and simply wasted the competition. What's more, Kaede jumped from Round 1 to Round 3 when her Round 2 opponents, Mana and Ku Fei, took each other out. So we really had no idea what to expect. Both very similar characters, being the 'smiling with eyes closed' types you see so often in manga, they are casually polite at the start, and then Ku:Nel decides to use gravity magic to simply flatten Kaede. Everyone gasps, and he wonders if he actually overdid things a bit. Then we see four Kaedes, all surrounding him, commenting on how awesome his power is. What follows is a fantastic battle, pure shonen grace and artistry, showing two equally matched opponents simply going at each other, tossing compliments the entire way. This is where you realize that Akamatsu finally did it - he has the fighting manga now, not the harem manga. And the audience love it.
5) Eva confronts "Nagi" (Volume 13). Akamatsu is very good at subtly pulling the heartstrings when he wants to. After a long battle between Negi and his "father" (actually a simulacrum created by Ku:Nel Sanders, but it looks, acts and fights just like the real thing), we're already emotionally exhausted seeing Negi joyfully living a reunion he never thought he'd have, false as it is. After thoroughly trouncing Negi, his father (who only has a short time before the illusion expires) tells him to live wife happily and prepares to leave. This despite Negi noting, to the illusion's surprise, that he's not dead. As if this weren't enough, Evangeline then bursts into the arena, confronting the man who she stalked for years (and who imprisoned her at the Academy). After some brief humor where "Nagi" finds that a) an evil vampire is his son's mentor, and b) he forgot to release her from the imprisonment, which wasn't meant to be that long, Eva tells him to shut up. Knowing it's only an illusion, but not caring, she asks for a hug. Which he refuses. So she settles for a pat on the head. This he accedes to, and we see her blushing, with tears in her eyes. This is, I think, the only time the entire series we've seen Eva cry. It's a beautiful moment, and shows you the effect Negi's father had on her.
6) Chao's past (Volume 18). After defeating Chao Lingshen at the end of the Festival, Negi confronts her before she returns to the future that she failed to change. He notes that the markings on her body, magical tattoos that drew an insane amount of power, and implies that these were put on her by force, a charge which she does not dispute. He then asks Chao about what happened to her to bring her to this point. At this point we're all expecting a long flashback arc telling us about Chao's past. But Akamatsu knows his audience is already exhausted by the Festival arc, so Chao cuts him short. This is one bit I'll actually quote in its entirety: "Negi-bozu... knowing a person's past doesn't mean you'll understand them. If you want to know about me, go read a history textbook or watch the latest news. My past is no different from the countless tragedies that happen every day on this planet." I talk here about good plot and character moments, or great tipping points. This is one moment I'm including as it's simply good writing. It sums up Chao better than any flashback could.
7) Negi punching Fate (Volume 21). The cliffhanger to Volume 20 was rather stunning. After arriving in the magical world, Negi's having enough trouble dealing with a bunch of stowaways without having evil villains around. But Fate is there, and decides to simply take Negi out there and then, with a huge stone spear through the shoulder. Negi coughs up blood and collapses in a heap. The others try to rescue him, but their pactio cards and weapons are all locked in a magical box which they can't open due to arriving at the Magic World equivalent of Customs. Then, the rest of Fate's evil gang show up and take our heroes to the cleaners. Powerful allies like Setsuna and Kaede are shown to be overmatched by these guys. Then Fate notes that he should simply turn everyone to stone permanently. As he prepares to do this, he is met with a left hook to the face from our hero, who has somehow managed to get back up and punch the hell out of Fate USING THE STONE SPEAR HE WAS IMPALED WITH. Every shonen hero needs a point to show that he's the hero. This is one of Negi's biggest.
8) "Super Magical Girl Yue!!" (Volume 23). Yue has always been one of the more interesting girls in Negi's class. At first seeming like the stereotypical 'emotionless girl', she later proves to be anything but, showing she's simply reserved unless around friends, or when she gets fired up. She's among the worst in the class for grades, but it's heavily implied that it's apathy and hatred of studying that causes this rather than any issues with learning. Now she's ended up in the magical world, and even worse she has amnesia. Luckily she's relatively safe at the world's largest Magic Academy, and quickly joins the school. Without her memories holding her back, and with a subject that actually interests her, Yue shows she's an utter genius, quickly leaping to near the head of the class in a mere month. This culminates in a marathon battle to see who gets to represent the class as Magical Bodyguards. Yue manages to out-think most of the class in taking the lead, then after her rival tries taking a shortcut and instead merely ends up awaking a killer monster, Yue calmly ascertains the monster's weak point, gets her rival to rain ice spears down on it, then uses her broom to FLY THROUGH THE RAIN OF ICE SPEARS and take it down with one stab of a knife at its one tiny weak point. Not bad for a deadpan flat-chested girl, huh?
9) Fate capturing [REDACTED] (Volume 26). This is the one point in the story where I actually try to hold to not spoiling, as opposed to simply saying I won't and then revealing all. That's because this revelation is utterly fantastic. It comes at the end of another long battle with Fate, which ended as most other battles have, with Fate retreating after beating the tar out of Negi, but with our heroes unscathed and with new information courtesy of Nodoka and her magical mind-reading. That's why it's all the more stunning in this volume to see that one of the characters has actually been captured and replaced with a copy, and Negi's party suffered its biggest loss yet. They don't actually know this yet, but we the reader get to be ahead of Negi for once as we see Fate's crew taunting their prisoner that in order to be rescued, Negi and company have to notice she's gone. In a series like this, you need your villains to be dangerous and feel like a threat. This was a huge step in that process. Negi's just lost one of his most precious allies.
10) Ako discovering that "Nagi" is Negi (Volume 27). And sometimes it's all about the heartbreak. Ako is first given an arc in Vols. 14-15, where she's romanced (accidentally) by Negi, who has taken aging pills and is pretending to be his cousin Nagi. Ako already has a lot of self-image problems to start with, and dealing with Negi's genuinely unconscious flirting (Chisame notes he's a 10-year-old "natural-born gigolo") makes her fall completely in love. Her self-image problems are partly due to a huge scar that goes across her back, which she's had since she was a child (we still don't know how she got it), and partly due to thinking that she's merely a 'side-character' in someone else's story, supporting the stars (such as Negi, Asuna, Nodoka, and Setsuna, for example). Having been dragged along to follow Negi and company to the magical world, she finds herself sold as a slave in order to buy medicine to cure a nasty disease she got immediately on arrival. But hey, she meets Nagi again, who's entering a tournament in order to free her and her fellow classmates who are also now slaves. Then she discovers that Nagi is actually her 10-year-old teacher. She at least manages to get away from him before breaking down, but we then see her in the hot springs, sobbing her heart out. For a series with tons of naked fanservice, there is for once nothing erotic about this - it's pure cleansing agony, and yet another in a series of horrific moments for this girl who can't catch a break.
I've left out so many, but this post is already getting a bit long. If you have any others to suggest, leave them in the comments! (Note: don't suggests moments that haven't come out from Del Rey yet. I'm well aware there's tons of awesome after these. Please support your North American publishers.) So, in short, Negima is awesome.