Touch Arcade: Megatroid's [Free] levels keep surprising me. They're almost universally well-designed, with branching paths and hidden rewards, healthy smatterings of enemies, and new and exciting insta-kill traps every so often. And the difficulty curve is really quite good. Aside from the occasional out-of-place spike, the enemies do a great job of keeping pace with my character's skills. These might be the sorts of things you'd expect from a Mega Man-style platformer, but there's a reason I'm impressed: Megatroid's levels are randomly generated.