Just a warning that Gamestop often increases prices for those 2 for 1 weekends. A game that might have been used for $19.99 last week will go up to $24.99, and so on.
Be best to check regular prices for new on Amazon before you go in there. Or after, and then go back if it is actually a deal.
Especially the Square DS games, are somehow regularly $40, so GS will sell a used one for $35 or $30, which is the regular new price everyday on Amazon...
Just be careful, don't get ripped off.