I haven't read Hana-Kimi yet, but I can definitely back up the recommendations for Honey and Clover, as well as Full Moon. They're two of my favorite series!
I'm like Radical Dreamer when it comes to the art style of H&C -- it definitely grew on me. I can't imagine it looking any other way (nor would I want it to) now. It's really sketchy and most of the panels look as though they were drawn in about 5-10 minutes, but that's what makes the manga so unique. I love it...but if that's not the case for you, at least the anime art is pretty. XD
Another thing that was refreshing to me (though I seriously doubt most people even care) is that the two main female characters, Hagu and Ayu, are often drawn in very modest outfits. Mostly longer skirts and dresses that are actually cute! Since a lot of female characters you see in anime/manga series look like they're only added as eye candy, with huge chests and all that stuff, it's something that stood out to me. Even in shoujo manga, a lot of the girls usually wear short skirts with their uniforms and outfits, so... yeah. *shrugs* I'm not saying we should dress like that all the time; I just think it's important that we stay modest, especially as Christians.
(Sorry this post sounds stupid, I'm tired. XD)