Let's first discuss Negima's genre and its harem label. Yes, the series as a whole is interspersed with somewhat excessive amounts of fanservice, although never in a way that feels creepy (as compared to, say, DxD). And yes, the 10-year old MC becomes the object of a whole class of middle school girls' attraction. But although it contains all the plot elements of a harem, the spirit of the manga is much closer to that of something like Love Live, or K-On!. Romance as a whole is a lighthearted concept in this series, and spoiler - nothing *really* develops for Negi outside of platonic friendships or sisterly love. The core of the emotional load in Negima lies in the girl-to-girl relationships between the members of 3-A, and not at all in some creepy situation involving a 10 year old, as many potential readers have been misled to think. So yes, Negi is an ever-present force in this story, but his "relationships" with the girls are ultimately for sentimentality or comedic effect. If I had to give Negima my own labels, I would probably say something like adventure, fantasy, shonen, and comedy with a touch of slice-of-life.
With that out of the way, let's move on to what makes Negima good: the characters. Akamatsu manages to take an absolutely gargantuan cast - 30 girls right off the bat, then dozens more as the story progresses - and develop them all beautifully. By the end of the manga, a reader knows 40-50 some characters by heart and will care deeply for at least several of them. I've rarely seen characters more memorable than those of Negima, and definitely not in a cast of this size. Even the villains, Fate and Ialda, are unique and easy to sympathize with. When it comes to character design and development, Negima is by far the best manga I've ever read and a masterclass in the subject.
Akamatsu's art is *extremely* clean and easy to follow, especially in the action scenes. Explosions or magical spells that would have been a visual mess in other series are handled with absolute precision in Negima. The character designs are cool/cute as well. This work quite clearly contains the peak of Akamatsu's artistic abilities, and it's a treat to be able to flip through the pages on this one. His art style and designs seem to stabilize around the Kyoto - school festival arcs, so do read until then.
The story is where things seem to be a tad bit loose, although not to any significant extent. The school festival and magical world arcs are an absolutely crazy blast to read through. However, the plot is admittedly slow in the introduction up to the Kyoto arc, partly due to the larger portion of slice-of-life type chapters. I'd say that this is more of a deterrent than a flaw, however, as these chapters are retrospectively essential in fleshing out the cast and giving Negima the classic all-girls high school vibe. The ending is also potentially a disappointment, with a few minor questions simply being timeskipped, as the series got axed by publishing disputes. Personally, I still found it quite satisfying and poignant. I feel that it would be hard to top the adrenaline of the magical world arc anyways, and it avoids ending up yet another shonen that redundantly loops conflicts to no end. But if you're insistent on seeing the conclusion to the Negima story, Akamatsu wraps it up slightly in UQ Holder ch. 137-140.
Either way, Negima is a criminally underrated masterpiece of a manga which you should not miss out on. With an unmatched combination of memorable characters and dramatic plot resulting from its unique slice-of-life/action hybrid, the universe takes on a life of its own far beyond its pages and will stay with you after you finish the series. As long as you can keep an open mind through its opening fifth and take the fanservice with a grain of salt, you will be rewarded with an epic but undiscovered story on par with the modern classics of the generation.
