I admit that I haven't tried 'just' a cupcake yet, but what I did try -- a "cupcake shake" -- was excellent! From the moment you open the door, your nose is inundated by the absolutely amazing smell of baking. (I don't know why this isn't common in most modern cupcake places and general bakeries, but they definitely get it right here.) The bakery case is filled with a large assortment of cupcakes and cookies. A counter to the left of the bakery case has pictures and descriptions of the _giant_ cupcakes you can order; think cake-sized cupcakes...or if you will, a cupcake-looking cake. There are also teas, hot chocolate, and ice cream. The last is used to make the excellent cupcake shakes, which are milkshakes with an entire cupcake blended in!
Colossal Cupcake looks like it's an older place or at least is in an older space -- it's comfortably well-worn, with kind of a quirky princess vibe. (Or as Lauren K. said, a Wonderland vibe.) I thought the prices were very good. I'd definitely return!