Hanihani's protagonist is Naoki, who lost his parents and his memory in an accident five years ago, and was taken in by his aunt and uncle. They have a daughter, Matsuri, who lives with them, and she's my favorite character in the series--in two words, the tsundere imouto. You'd think Matsuri would wake Naoki up in the morning, or he'd have an alarm clock like any normal single guy would wake up to, but instead following bishoujo game convention it's Naoki's childhood friend Honami who always wakes him up. He seems to have a pretty normal school life--at least until a transfer student named Mikoto literally drops out of the sky on him, which he writes off as some kind of hallucination. Naoki's life isn't perfect though, since he's bothered by recurring dreams of a post-apocalyptic world...and while at first the anime takes us through the usual episodes focusing on each side character in turn, towards the end it turns out there's something serious going on...
In the end, not to go into spoilers, but for me the greatest weakness of Hanihani was its plot. It's not Kanon, it's not Da Capo, it's not even Gift or Shuffle. The plot's not really bad or anything, it just seemed a little far-fetched to me. I won't try to poke holes in it, because if you watch it I don't think you'll have any trouble doing that yourself. But in Hanihani's defense, it does have a very likeable cast of characters--AugustSoft is the same company that brought the world Feena-sama from Yoakena after all. Mikoto, Honami, Matsuri, Yui-sensei (their homeroom teacher, who like Mika in Sensei no Ojikan is about three-foot-nothing tall) and the rest of the cast are all fun to watch and have their own distinct personalities. Usually I can tell from just watching the opening credits who the winner will be (whichever bishoujo gets the most screentime and/or is in the middle at the end = winner) but to its credit Hanihani keeps you guessing until towards the end when the serious part of the plot kicks in.
Hanihani's male lead actually makes a decision during the course of the series on who he likes too, and doesn't waver endlessly like other examples in the genre, which is another point in Hanihani's favor. The animation quality is so-so (but better than Cabbage Love by far) and while the character designs can't compete with the game counterparts, they're still easy on the eyes. Speaking of the game, insani has translated the Demo into English so you can play it (which I did)--and don't worry, it's work safe (in that there's no ero content--although unless your boss is really unobservant I can't say playing a bishoujo game at work when you should be working is really "safe").
It's not the greatest bishoujo series ever, but for a reason that's hard to pin down, I still really enjoyed Hanihani, enough that I gave it a re-watch. Maybe it's partly because I played the demo so I got to know the characters a little better, or I liked the fact it has a conclusive ending (with a wedding set five years after the rest of the story), or it's just because I'm generally a sucker for romance/bishoujo anime. Your mileage may vary, but especially since it's not all that long I think Hanihani's worth checking out.