Some similar anime I have seen with scores: Toradora!(10) Nana(10) Lovely Complex(8) Baka and Test(10) Seto no Hanayome(6) not a style of comedy I like.
Story: 8 The story progressed quite quickly. The main brother sister relationship with Kirino (sister) and Kyousuke (brother) grows and progresses through many incidents, and you feel them getting closer and closer, and that Kyousuke really tries to be a good brother. I really enjoyed their relationship and felt it was endearing. There are also a few twists and turns that keep the story fresh and interesting.
Characters: 9 The main protagonists (Kirino and Kyousuke), and Kuroneko get developed quite well, and they feel interesting and understandable. Kuroneko's character I fell in love with, she is such a great character, and so adorable for the first time I understand moe, a pure innocent little sister you want to care for and protect. She is now one of my top 5 favorite characters in anime (I've watched 100's). As for Ayase and Kanako they needed to be developed more for their actions to make more sense. Also a little additional background to Kyousuke would have helped make him more multi-dimensional, and Kirino is a little over the top with her tsun side (hitting, angry, and denying) making her character less believable.
Enjoyment: 9 This anime was a joy to watch. Most of the episodes had at least a few jokes in there that made me laugh quite a bit. The jokes are great and well thought out, and are not slapstick. This is one of the funniest anime I have seen in a long time. There is also great fun poking at, commenting on anime, and the examining of Otaku culture. Also I remember feeling the tension once or twice thinking "no way." The comedy combined with developed characters and interesting relationships made it addicting to watch.
Overall: 8 It would be nice to read some of the light novel first to get a little extra background for Kyousuke and for Ayase and Kanako, and see a softer Kirino not so tsun (hitting, angry, and denying), as in the light novels. Those and the ending are the main negatives to the anime. Overall the plot, characters, comedy, and relationships were great. I think I would maybe even re-watch some episodes for the laughs and Kuroneko, and I almost never re-watch anything.
Ending: 6 The ending is okay till the last 3 minutes of the ending, which outraged pretty much everyone, including myself. There is a reason, the publisher wouldn't let the author write the ending he wanted, which is in the link. Many say the real ending is in the Tsuzuku PSP game, look on YouTube and look for dizzy ziddy's play through. If you watch the play through of the last chapter(s) and read the interview, you should come away feeling okay about the ending, but not thrilled either.
Interview with the author about the ending restrictions and what he tried to convey. Link has SPOILERS!!!!
http://anime.stackexchange.com/questions/4901/why-did-the-until-we-graduate-provision-enter-into-the-ending-of-oreimo
