Best of the series!
For its time, TMNT surely has a varying gameplay. It consists of a few main elements; team play, learning the routes in each stage, learning your turtle's abilities, and getting the most of the bonus weapons you find. If the player considers all these elements, he/she will find the game very enjoyable. Every turtle has it's strengths, Donatello is the strongest and his bo is long, Raphael is the second strongest and fastest making him very useful most of the time fighting through varying enemies and giving that intense close combat feel, Leonardo is somewhat strong and pretty fast making him useful against large swarms of little enemies, Michelangelo is the fastest but also not good for reaching enemies above him. The turtles walk slow, but their jumps are well coordinated by either pressing, holding down, or giving a tap for the A-button. TMNT stresses the team play element. You must switch between your turtles at all times. Not knowing this makes the game hard for many players. Learning the routes is not so fun, but not too hard either. Usually improvising will get you where you want a part from a few dead ends.
As for the challenge, TMNT is usually considered frustrating. However, learning the stages, different routes and bonus locations is a part of the challenge without which any player feels stuck and lost much like in a Zelda game. There's that adventure element that the player has to work through. Some of the stage layouts in later stages are very challenging yet revarding after you've beaten the boss. You will loose a fair amount of energy along your way but there are endless pizzas to keep you going and you can even get your defeated turtles back in certain areas. The biggest complaint here are the almost impossible traps in the final stage and a few sewer layouts in level three right after the dam-stage. It is a challenging game but even as a young player I didn't find the game impossible at all, much less today.
Over all, TMNT is a classic that gives the player something that almost no other game gave when it was released with its original stages and rare but fun top down sequences. It's not a game for someone to just try and run through but it is very rewarding if one takes time to really learn to beat the challenge.