Exciting, bombastic action. You nailed the real retro arcade feel.
I feel the controls could have been more responsive, but then that is part of the challenge. It just seemed to take slightly too long for the jetpack's lift to kick in. I also struggled with the camera when moving left to mop up remaining enemies (which was a bit frustrating, but true to its origins).
It was just too hard for me, too. I'm not much of a fan of challenging action games. I enjoyed the experience, though.