Finished an introductory pass through Haganai P, received the default end ("sisters battle").
Overal impression is mostly positive. Story is not terribly dramatic, at least on the path that I hit, but it's all right.
The plot graph is branchy like hell. I dread restaring and taking it seriously. The difficult part is that effect of selections is entirely unobvious. There's no Inko to give you a seed. Also, on the map there's an issue of combinatorics: it does matter whom to talk to first, whom to talk to next. Getting ends of this game is going to be much more laborous.
Unfortunately for those with weak Japanese, there is a lot of reading, despite the voiced protagonist. It comes in as "narration", or Kodaka talking to himself. Toradora P did not have anything like it. Even more unfortunate is that the post-ending hints are given by Tomo-chan, who is not voiced. Brush your kanji and grammar.
One technical detail: for some reason, there is no battery indicator in the pause screen.
UPDATE: At Meenuvia: Yozora and Sena (separate endings), Yukimura and "IF", Rika finale (the best end).