Just bought this today, since it apparently came out recently. I haven't played much, just the tutorial and the level immediately after. The graphics aren't bad, a little lower res than the console versions, but...
The music so far seems to be all recycled from We Love Katamari. Granted, the songs aren't BAD, but it would've been nice to have new ones. Maybe there are new ones in later levels, I dunno, but the two levels I played had recycled songs.
It would be nice to have a run feature for the menu. It's kinda big, and it takes a while to walk from one end to the other. A minor complaint, but still.
My biggest complaint has to be the controls, though. I know, they did the best they could with the PSP, but this is why they shouldn't have made a PSP one. The controls just aren't as natural as they are with the PS2 controller. I find myself taking forever to make a turn, or only after the fact realizing I have my finger on the wrong button to move forward. Maybe you get used to the controls after a while. I don't know, but first impressions are very poor.