Kanon - The ending didn't really make sense for me, it was never properly explained what happened..
Kanon and Clannad - The focus is on the least interesting (in my opinion!) of the girls in both series.. both could have been better if they'd given more time to the other girls.
Clannad ~After Story~
What the hell!? They just came back to life? What was that!!? That just annoyed me -_-"
Elfen Lied - I absolutey love this anime, but if I show it to a friend and they ask "Why all the nakedness?" I can never come up with a satisfactory answer.. it seems a bit pointless..
Aria - President Aria.. he had his moments, but generally I found him annoying, especially when episodes focused primarily on him.. also I think some of the side on shots of the characters looked a bit iffy, perhaps some better character animation would have done a better job..
Lucky Star - Lucky Channel... fail -_-"
I could go on for quite some time, but I cba...
Always happy to chat :)