Zone Runner 2 is a very simple yet extremely addictive game. The concept is simple: run through the zones, while collecting the gold coins and avoiding the obstacles. I'll admit it's not the most original game, but there's something about it that keeps you hooked.
There are 30 stages total, with 10 stages in each of the 3 zones. The game will save after every zone you complete. There are various obstacles, consisting of mines, platforms, and conveyor belts. As you progress through the game, more of these are introduced (the first ones show up after the 2nd level).
Overall, ZR2 is a great game. It's challenging enough to keep you hooked, but not so challenging that you'll give up and throw your computer out the window. And you might also want to check out the prequel, Zone Runner.