My biggest hate is the 12-episode series for sure.
They are really killing great series by cramming so much into these 12 episodes, but at the same time it's mostly just filler crap.
They aren't actually telling us much of a story or really showing anything. It mostly just seems they put some boobs on screen and want to show off their artwork, that's it sadly
RE: Ask Anime Week #54: What's the bad and popular trend you noticed in anime?