Then I realized that not only can you play the pre-made game levels -- you can create your own levels. You can then play your levels and the levels others created. There is also a rating system for levels so you can find the good ones and get ideas for your own creations.
I usually play a space shooter for a few minutes and then tire of it. Zeta Flow has a lot of replay value so you may find yourself wasting time for hours with this little space shooter gem.