Beelzebub, did i mention this before? Its really directed to the ending, that's all. (Granted, the manga pretty much didn't do that much better, i havent read it recently so i wouldn't know that much.)
0-7 Ghost, this is one of those situations where i liked the anime, but it pretty much mind fucked me by ending it in the middle of nowhere just to get popularity for the manga...wtf?
Myself; Yourself, idk if anyone has watched this before, but seriously i felt completely nothing from watching this, idk what it was...the plot was quite sad, but it didnt appeal to me, heck im surprised i finished those 12 long hours of hell.
Shinkyoku Sokai Polyphonica, Honestly, this anime could have gone somewhere if they put more emotion into it, and what do i mean by emotion? Really that's a answer that differs for everyone else since i completely throw away an anime that doesnt have a good OST backing up those epic/sad scenes to really spice it up, i mean Air Gear? Art not so much but Chain by Back-On made everything possible.
In the end, so many animes disappointed me and made me regret watching it, but most of them were because of a single bad thing.