The gamestop in Laurel, MD, on two separate occasions, denied that I had pre-ordered games (Fable 2 and Halo 3), despite having the receipt. That particularly bothered me, but I'd only put $5 on them, so it didn't hurt.
I have had good experiences, mostly, though. I don't generally buy stuff from gamestop unless it's a pre-order that I really really want (fallout new vegas, MW2).
I was about 11/12 when Funcoland went out of business. I remember being very very sad about it. I used to love going to the store and getting the funcoland newspaper that had all their games listed, with the game's prices and finding games that I wanted that I could afford. That, to me, separates them from Gamestop. Gamestop, so far as I know, does not publish current game prices or trade-in values.
The majority of my business now goes to Movie Trading Company in Fort Worth, TX, or Book and Music Exchange in Louisville, KY. They will generally beat out Gamestop's prices, and they also carry Sega CD games. I'd forgive Gamestop all their sins if they'd carry Sega CD games. XD