I think Hana Kimi was the second manga I ever read, and it's the reason I got hooked on the whole franchise. It's amazing. Amazing, amazing, amazing. I can't even describe how much I love this series - I've read the whole thing at least ** six times** now, and it just never gets old.
Art: Beautiful, simple, and I especially loved the flowers. You can't tell it's from an older generation of manga at all. (I actually like this style a lot more than some of the newer stuff, with the enormous eyes that take up half of the face.)
Story: So original that I almost want to say that every gender-bender manga has copied this in some way. (Only this tops all of them anyhow.) The pacing can be slow sometimes - well, sort of. There are filler arcs, I mean, but it's not that the relationships don't develop during them; they just develop more dramatically during other parts of the story. And the entire manga is so funny. Like, I'm laughing out loud most of the time I'm reading. It's awesome.
As for the ending . . . I actually liked it. It wasn't too abrupt, although it almost started that way, but you could tell when the manga was winding to a close. And the way it went down really seemed to come out of the blue to me. I'd really thought I knew exactly how the Hana Kimi was going to end - when it twisted. And the omake at the end was really sweet, and I felt it really tied up all the loose ends.
Characters: I love them all. ALL. Ashiya because she manages to pull off being an innocent, cheerful, completely-oblivious heroine without annoying me; Nakatsu for being the comic relief/
love-rival
/best friend character who everyone pretty much has to love, Namba-sempai for being the most awesome playboy (with a reason! How often does the playboy character get a reason for being a playboy?) yet still being a nice guy and a trusted older brother figure, Nakao-kun for being such a gosh darn cute, adorable little tsundere...
...And Sano, for being the God of Sexiness. Because he is. Lovelovelove. Best bishie ever.
Downsides? For me, personally, there really aren't any, but I'll list a few things other people might find annoying.
It is cliche - optimistic, oblivious heroine, love triangle, school setting - but only because it almost created the cliche. There are quite a few filler arcs, which, while I find them funny and certainly worth having, do drag out the story a bit. And, there isn't a whole lot of major conflict: They have their problems, but they aren't big and dramatic, and they generally only take a few chapters to resolve. There is very little angst in Hana Kimi, so if that's your thing, you might not love this.
Just read it, okay? Please? It's so amazing, it'll be worth your time. (I'm off to start re-reading it for the seventh time 😀 )