Pretty cool.
I haven't played it all the way through, but it's pretty awesome.
good: You don't have to worry about lives, which would just be annoying in this game; simple yet wicked-looking graphics make great characters without loking cluttery and such; and general awesomeness (how the levels are made, the upgrades, etc...).
Bad: Not being able to jump within the circle is annoying sometimes when I try to avoid spikes and buzz saws and such; not as addicting as people say it is, but that's probably just me not being easily addicted.
Overall, it's pretty good, since not being addicting is just me, not the game, and you probably did the no jumping over stuff on purpose. 5/5