Pro Unlimited playability
There's 3 difficulties. Easy, Normal, and Hell. Easy would be for the ultra-casual player, or perhaps a player that hasn't played something similar before. Normal is where you'll find most people, as it's challenging but overly so. Hell mode is one you don't take too lightly, it's pretty ridiculously hard. On top of that, Gauntlet gets harder and harder every time you clear a map. You can play over 40 hours and still enjoy yourself.