Obviously it's packed before Halloween, so plan accordingly. i thought they actually did a fairly decent job of handling the chaos while I was in the store. The lines are long, but given the amount of people in there, duh, you're going to have some wait time so don't try to go the hour before the party...my bad.
Overall, they do have a varied assortment of, go figure, party supplies and costumes.
At less busy times, it's easier to maneuver and you can get in and out. For $25 i got a serviceable Santa outfit for Santacon. For Halloween, i got a crappy mustache that didn't stay on all that well, but they have enough props and stuff to make a decent outfit.