Teenage Mutant Ninja Turtles is a decent game that provides some challenge while still staying close to the show.
The game was unique in that it allowed the player to explore an overworld and enter small dungeon-like areas like buildings and sewers. These dungeons are two dimensional and are mostly platforming in nature. Also, players could switch between available characters at any time.
Even for being a children's game, TMNT is fairly tough at some points. The bosses at the end of each level are relentless and most of the regular enemies inflict a large amount of damage.
Teenage Mutant Ninja Turtles is a great game to play if you enjoy the cartoon or the comic books. Although its a bit difficult and based off of the light-hearted show, it makes for a decent experience.