Prepare yourself for feels, because that's what Angel Beats brings to the table. This is one of those animes that everyone seems to like, and yet everyone who writes anime reviews really seems to hate. This is the case with much of the creator Jun Maeda's previous works as well such as Clannad, Air, and Kanon. As people have come to expect from those previous shows, there is a main character lacking any particularly remarkable character traits in which the viewer can just jump right into his skin surrounded by a variety of mentally and physically broken girls. At some point one of these girls dies of a mysterious illness. Angel Beats is essentially where all those characters go in the Maeda-verse after they die.
In Angel Beats, everyone is already dead. It's not a spoiler, they say so in the first few minutes of the show. The main character Otonashi, with all the personality of a a beige wet dish rag, ends up in a school yard with no memory of how he got there. Suddenly, a girl with a large gun announces he has died and tries to recruit him into her underground battlefront to fight against the unfair God who tortured them in life and the afterlife. In this world, they fight against Angel, who is a solemn and emotionless robotic type of girl who has abilities to fight them.
From there on out, the main characters as well as a long list of side characters go on a series of whacky, funny, daring, sad, angsty, and sometimes philosophical adventures. Sounds like too many themes and genres for just one 13 episode anime, right? That's what everyone says. A major complaint is that Angel Beats tries to please everyone--comedy fans, drama fans, seinen fans, romance fans, slice of life fans--all those people. As a fan of all those genres, I found it supremely enjoyable. I loved laughing one episode and being on a verge of tears the next, it was really quite a rollercoaster.
My one major complaint, is that they did not spend enough time on all the characters. Everyone in Angel Beats has a sad story of their life, but you only get to hear about a fourth of the stories. Even in the Light Novels, the author doesn't expand on the sad stories of characters like TK or Takamatsu.
However, characters aside, the show does stun with it's bright and energetic animation and catchy music. However, while the rock songs by the battlefronts distraction band Girls Dead Monster are stupidly addicting, when the anime came out in 2010 they incessantly released singles to go along with the premiere of episodes. It was essentially just trying to capture the K-ON popularity in that way.
Overall though, if you can look past the traditional personality lacking main character of Jun Maeda's usual work and some sadly lacking back stories, Angel Beats is a fantastic rollercoaster of emotion with an awesome soundtrack. Perhaps I have an odd biased as I watched it when I was getting ready to graduate college and the ending kind of really hit close to home.