Personally, I felt that whether or not players could stick with the game's challenging controls until they got their hands on the TILT JET would be the deciding factor in whether they continued playing. And by the time they've acquired the MK.III CRAFT, I think the option to quit playing is pretty much gone.
Filling out the upgrade tree is a really exciting experience, and I find myself wanting to give it another try time and time again. I had to put it aside partway through due to time constraints, but it's the kind of game that makes me want to come back to it. 🙂