I haven't played the whole game, but I've played the first 4 or so levels (borrowed a friend's PSP) and it was very fun. For a PSP game, the controls are very good, the graphics are impressive, and the gameplay is great as well. Even though it isn't made by Insomniac, the developers did a very good job at keeping the traditional feel of the series. The only really bad things I've heard about it are the length (too short) and the multiplayer which is a bit lacking. I'd say that for $15 its a great deal.
EDIT: Just wanted to add that they are releasing a new game called Secret Agent Clank. I think it comes out sometime within the next few months, and you get to control Clank (for basically the whole game, if not the whole thing) who supposedly has all kinds of cool gadgets and stuff. That might be worth checking out too when it finally comes around.
