Hah, I once made something katamari-like on a 2D-plane as one of my Experimental Games - but what you have done seems to be much better!

Aside from the too-simple graphics and proportion-issues (which are all likely removed until it moves past "almost alpha"), I'd think it'd be cool to let the things I've picked up move smoothly to its place, instead of it popping up there. (It would feel more like "building it up" then)

I also totally don't know how you did that, but if it were me to code that, I'd probably have an invisible model run around and assign the objects to random vertices and align them using their normal. If you do it that way, then it'd be cool if you include other models (or shapes if you do it differently ) as well: I'm at a beach? Then make me reveal a small crab. I'm in a garden? Then I could reveal a small bird... you know, these kind of things. Then let me unlock them (when more than 80% of it is revealed or something) so I can play them in a free mode wherever I want! Horray! it's an amazing idea!

Or... maybe it's not. Whatever. Will you make the music dynamic? I become bigger, I hear more tracks, or something.

All in all, looks great!