I finished all 8 levels with the best possible ranking, and beat level 8 in the cream suit for the super awesome secret bonus.
It's a really good game, though, I highly recommend it. Simple, yeah, but lots of fun! And it's even more fun when you get the commando suit and have the stealth upgrade, because you're invisible to everything except lasers.
(Of course, you have to best the first 7 levels with perfect rankings to _GET_ the commando suit, so it hardly does much
)