Every Pokemon game from the fourth generation until now (and probably until forever). I keep letting myself play them, gen four was horrid, gen five wasn't as bad but it wasn't very good, and gen six is probably only better (to me) cause I like when I can play dress up with my characters. I keep letting myself waste 40-50 or how many ever hours beating the newest release but I regret the buy every time. I know when X²/Y² / X2/Y2 / Z comes out, I'll probably play it through.
I know I'm not the only one either.
Game(s) right now: Dragon Quest VII: Fragments of the Forgotten Past