Imagine you wake up in an unfamiliar place, having lost your memory and being told that you're dead.
Welcome to Angel Beats!
The story of Angel Beats! is very deep. Very deep. It covers topics such as child abuse and situations where people have watched their loved ones die right in front of them. It covers these topics in a mature manner, with the occasional gag or joke to add a bit of comic relief to what may otherwise else be a depressing storyline.
The actual idea of waking up dead, per se, in the afterlife is one that is not explored often in anime, and so provides a unique twist to a potential slice-of-life anime. The familiar setting of a school draws you in, and helps immerse you in the story, as it is a common setting amongst anime.
The multiple genres of Angel Beats! are expertly fine-tuned to have the correct mix of each one. Action, comedy, slice-of-life, even music at times! The resident band is a girl rock band named: Girls Dead Monster. The band is used not only to provide music, but also as a tool for the other genres in the story. For example: GDM perform a concert to the 'students' (who are actually NPCs), while the members of the Afterlife Battlefront (the protagonists) carry out a mission.
The reason why the story only gets 8/10 is because holes are left in the story regarding the past of a few characters. Perhaps an After Story would solve that issue, but no announcements have been made as of yet.
Animation and Sound:
I'm gonna be short and sweet here. The animation is fluid and immaculate, especially when Angel's abilities are activated. Perfect use of different camera angles and speed settings add to the drama and suspense before and during a scene. The sound I'll mention is the music. The opening theme is a beautiful piece played on the piano, sung by the character Angel. The rock stylings of GDM are a nice touch as well, starting an action scene with a song, and switching views between the fun of the band and the action of the fights.
I'm not going to go in-depth with each character. The Afterlife Battlefront are a mix of different personalities. A very rag-tag bunch of soldiers. Whether it's the logical and curious protagonist, the joyful Yui, the stoic but cute Shiina or even the eccentric T.K, Angle Beats! has characters that everyone can relate to in one way or another. No one is left behind, if you'll pardon the pun.
Overall, 9.5/10. It is my second favourite anime of all-time, and I'll admit manly tears were shed by the end, but I leave that up to you to watch and feel and whatnot.