Unoriginal, but Brilliant!
This is the only game I've opened more than once on Newgrounds, and that really says something. I've played the heck out of the original Super Mario Bros, and the crossover idea has been juggled around for ages... However, this game has nailed it! The attention to detail of the original Super Mario Bros and the crossover characters is simply amazing; you can tell the author is no amateur!
My only gripe is that all the characters that are available (with the exception of Mario) go the same speed: slow. I constantly finding myself racing the clock instead of enjoying myself. Why not have some more characters as well, not just crossed over from Nintendo games, but maybe Sega? *cough* 8-bit Sonic *cough*.
Still a minor gripe, but it's no reason to not keep coming back and playing over and over again, mastering the levels with each character! Perfect 10 from me!