A very cool game concept!
I loved playing this game. The graphics are fun, the animations are smooth, and the sound effects are appropriate.
It's a darn good thing there are several levels open at the start or else I'd have given up a lot sooner. These levels are HARD! I was only able to complete the first level in target mode so far, but I plan to try again later.
I think the levels could use a little tweaking here and there. For instance, everything is so far apart it's very difficult to tell what might happen to McNuts once he is launched from whatever contraption he is in/on. I like the pinball/trampoline concept, but the possibility of getting McNuts where you want him seemed to turn into a random probability equation. I think if you had a readout of the angle and power of your shot that would help decide what to do for the next shot. Of course that would detract from the arcade style of the game.
Also, although I found the sound effects very apt and fun, after playing a few levels, they had repeated so many times, they got pretty old. The same can be said for the truck which I saw a zillion times.
Overall, this is a great game. I'm sure the user made levels or other add-ons are cool too, but to be honest, I'll never see them if they require going to your site. I Just visited your site for about 20 seconds and will never go back again because of all the popups (in Firefox no less! Is nothing sacred?!) You lost a potential visitor/customer with that annoying bullcrap.