top of the list is for sure selling open games as new. that is such a crock of shit, and they should be sued for it.
oh wait, there was a lawsuit about it already!
very close second is the customer service. I am sorry you think that you know more about video games than me and I have a crappy opinion of what makes a good game.
seriously, I pre-ordered Soul Calibur III for PS2 waaaaaaaaaaaaaaaaaayyyyyyyyyyyyyyy back and when I went to pick it up I was told that I "don't want that stupid game, its sucks. Buy this Resident Evil Chainsaw Controller!"
yea, don't shop there much since (only if its a cheap hard to find game).

Gamestop, ruin the damn industry.