@imtoomuch: I think jofaba hit the nail on the head. The secret to any game is to find the 10 second hook, then stretch it out over a few hours. I accomplish that by adding new gimmicks at each level, so no level offers the same gameplay and no level will play the same twice.
I think anyone who plays the game can come up with a good idea, something they'd like to see. I have such a huge list of gimmicks that I don't know where to draw the line and save them for another game.
@beenz: Glad to hear! The achievement system apparently isn't working, look for a fix this weekend- that should add even more replayability.
I plan to keep the game interesting by tieing Episodes, Bonus Levels, and Achievements, into a reward system to help you in Survivor mode, which will be the final update for the game (not for a few months.)
Look for an update this weekend with more goodies.