Story: I am absolutely certain that School Days is one of the few anime that will have you go WTF towards the end and make it so memorable, you would praise it till no end or will never ever touch it again. For me, its both. Starting off with an innocent love triangle, gradually transforming everything to a messed up psychological game of *no longer* love. In just 12 episodes, it captured perfectly how F-ed up love can become.
Animation: The overall animation is fine. Notice the odd camera angles?
Sound: I never paid much attention to the OP/ED, but the voice expressions were pretty good. The background music at some parts made the show some kind of epic drama.
Characters: Now, this is the kind of show that gives most credits to its characters. It would be the first time (if you hadn't) make you want to get rid of someone so very much. That is how magnificent the characters are.
Overall: School Days, is definitely a must watch for hardcore sadists and/or yandere fans.