Viewtiful Joe ROCKS. I got the game about noon on launch day, and I sadly had already beaten in on Adults(Note: PLAY KIDS FIRST, adults is OBSCENELY HARD. I wish i didn't try it.) and now I'm going through it again with the second character you unlock (and it hints towards more!)
The game only gets better, a few levels, (such as 5) were aggrivating with the lack of savepoints, but once you understand how the game works, you can easily get past them.
the bosses are BRUTALLY hard, perhaps its just because I played on adults, but they were definately the most difficult part of the game, certain bosses (level 6 *cringes*) took me HOURS to beat while other ones (level 4/5/7 mainly) were some of the best boss fights I've ever fought against in a game. The game also looks great all the way through the end, and some of the puzzles make you think... but not too much.
Definately a must buy, espicially at only 40$