Hey there,
I REALLY love this game. Played the first level, and fell in love on the spot. I have an aging 32 meg card (in my Rev A 15" imac), so I just turned all the graphics down to lowest to get the best framerates. With this type of game, the blocky style fits fine anyway. I got about 50-60 fps on level one.
I jump to level 2, and my framerates drop to 5-10 fps - with everything still at the lowest setting. Any reason why this might occur? It's unfortunate, I want to buy this game BAD, but the frame rates make it unplayable.