Little Busters! EX

Out of all the seasons of Little Busters, LB!:Ex is propably the most similar to Angel Beats, mainly because of the first "Arc" of Ex. We have a girl fighting against some kind of force on the grounds of school, the main guy helping her out and then them trying to find something in the underground of said school - meanwhile trying to dodge several traps etc. The similarities go on like that but to keep this spoiler free I won't go into more detail on this - you know what I mean by Angel Beats and the first Arc of LB!:Ex being pretty similar anyway. The other seasons and arcs aren't just as obvious with their similarites but still, since both are tear jerkers with kind of over the top characters and supernatural elements, you might enjoy one if you enjoyed the other.  read more 

both have short mystery arcs and wishes in both are so powerful that can change their worlds 

Both anime start off seemingly as a slice of life, but actually are both situated in worlds that have more to it than meets the eye, with antagonists in the shadows aiming for the main character's life. Both anime have the main character grabbing a baseball bat to defend himself when he feels threatened by something observing him from a distance. Both main characters have cute girls attempting to kill them constantly for a deeper reason than just mindless violence. Both shows revolve around the theme of friendship and youth, with a mystery element.