The basic story of Angel Beats is that a guy dies and finds himself in a sort of replica of normal life however he can not die. There he meets a group of teens who are fighting against a girl named angel. Story doesn't progress from there until quite a while, when it does eventually its pretty cool.
The animation looks solid. Nothing jittery or wrong with it, they even dabble with some slow-mo and fun neat tricks.
The sound is great. Here is where most of the passion for the anime came from, after all it is called angel BEATS. The in-show music is great and they put emphasis on the characters in the anime who play music, they try to capture the character of a musician and they do that really well with the Iwasawa. (The voices can get annoying but I watched it in english instead of subbed)
Characters vary. I think Yuri is not a good character but the makers obviously disagree because they spent a lot of time on her, I think they figure it out later because she gets less screen time later. Most the characters are pretty great, this anime spends a lot of time on backstory for each one instead of allowing us to really get to know the characters through current moments, but that is there choice.
Overall, some of the characters really pull this anime back from being really great, it seems like the begining lacks insight and spends too much time on being cool without planning ahead. Most of the characters stay flat and underdeveloped but that is to be expected with so many characters and so little episodes. Also the universe suffers from loopholes and such. When they gain new members to the cause they never discuss if the person has always been there or not, which if the character was always around that goes against the way they survive. The anime suffers many small flaws like that. Do your best to get past them. This anime isn't super great but the concept is neat (when not contradicting) and some of the characters (like Iwasawa and Otonashi) are really well done. It took me until about episode 9 to actually enjoy this anime for more than one episode at a time sadly.