^^ Please, do yourselves a favor and don't go to the one in Manhattan. There are stores in Brooklyn and NJ as well. Its really just awful choices, prices in the Manhattan one, plus its full of pushy tourists. If you go to the C21's outside of Manhattan they are always well stocked and relaxed. I've bought $9 Helmut Lang shirts, and got my K by Karl Lagerfeld trenchcoat for $79, not to mention the Dries Van Noten shoes I've got there for a pittance. I think C 21 gets bad mouthed so much because of how awful and high priced the Manhattan branch is.
The TJ Maxx stores and Marshalls here are just awful too, worse even. The clothing is really bad and the products they have for sale look they fell off a truck, dragged through mud and trampled on. I'd pick Century 21 over them any day.
And the C21 in LI has curtains if you're shy. I don't really care though if you just want to get in and change quickly its better than having to wait for a room, and its the same way with Loehmann's with the 'no curtains'. (Also, this is where I get all my deeply deeply discounted Vivienne Westwood).