Yeah, it's simple, and it's flawed, but it has its charm.
The story follows the show, starting from the end of season 1. The turtles have come to battle shredder to finish him off, once and for all. After that, they go back to the underground, get shot into space, journey through ancient feudal japan, and come back to new york city to finally destroy shredder.
The gameplay is what turns many people away from playing this. The game has newer graphics, but simple combat controls like you'd find in an older arcade game. The thing is, that's what games 1-3 are based on: arcade style play, with a newer look. When you start out, you can pull off a basic three-hit combo by pressing A, A, B in succession. As the game goes on, you collect crystals that temporarily boost your attack, defense, charge, or shurikken attacks. Those same crystals are also permanent power-ups. Once you collect 10, you get a permanent boost to one of the afforementioned stats. There are 30 of each crystal in all, and it really isn't a bad system of collecting to power up. You can aquire new combo moves by getting more crystals too. You can double jump, throw ninja stars, hold the attack button to charge a super attack (also powered-up by crystals), jump attack, and wall jump. Along with crystals, you can also find antiques. These items can get you concept art, some extra story, and eventually the original ninja turtle arcade game to play freely (a very well done port). Also, the way of navigating through the levels is set up on a big, yet organized map. All you do is choose where you want to go.
The fact of the matter is that the game can be too slow for most people. You run through big environments at a semi-slow speed. The enemies appear, and you take them out with the simple, yet effective, combos. If you play with more people, you all share the same health bar (probably the worst feature). In some levels, you ride hover boards and try to collect as many tokens as you can. By yourself, it's no problem, but with another person, you constantly bump into one another, usually causing you to fall off a cliff edge. While it can be frustrating, these levels add a lot of fun and humorous moments to the game. Bosses can be tricky as well, and usually require some strategy and a decent amount of skill to take out. There are tournaments to enter also, with one goal: survival. They are challenging, but can be pretty fun.
The environments look good and are well thought out for each situation. The enemies aren't bad, but they could be better. The music is catchy at times and the graphics are decent. The characters are good, but the tacked-on anime clips look awful (which is forgivable). Still, if you can look over the shortcomings of this game, there might be something here for you.
Overall, I say rent/borrow it first. It's not a terrible game, but it isn't one that everyone would like. Cheers!