Teenage Mutant Ninja Turtles for the GBA has very solid action. I selected my buddy Raphael, and was immediately getting into beating up on thugs.

B attacks, A jumps. The R button, or A and B together, does the turtle's special attack. It sounds simple, but there's more to it. There are standing, crouching, and "up" attack chains. Down and B twice does a sweep combo, standing B does a 4-hit attack chain, and up+B will knock an enemy into the air, which is followed by an air combo. With a little practice, anybody can chain various combinations of crouching, standing, and jump attacks. All of the attack animations are very stylish and ninja-like.

The game takes place entirely on a 2D plane. Walls can be scaled, and there's a double-jump. The enemies weren't particularly difficult. In the level I played, I scaled a lot of buildings and was able to jump back down to the street without any damage from falling.

Overall, it feels very much like the original NES and SNES TMNT games, except for being on a 2D plane. It might not be very hard, but it's still pretty fun.