School Days - I hated everyone with my soul, only felt a little sorry for Kotonoha, but she and everyone were stupid and/or a douche/whore. The ending was awesome and the only good thing about it. That was a nice boat.
SAO - Expected badass MMO anime,whe have the first half aaaaaand it's a shitty harem! Kirito is OP just because, forced incest and Asuna who had potential became completely useless. Hope they make something definitely NOT like the second half on the 2nd season.
Gantz - The protagonist was a piece of shit, and worst ending ever. I get it, there wasn't source material but they could have made it better that that.