This game is a complete letdown.
The game play is bad, but not too bad. It is playable, but only to a certain extent. You start off as one of the four turtles, and begin in the middle of a city. This is an overhead view. Then you either go into sewers or buildings. There are vehicles being driven around by the enemies, and the occasional enemy, but nothing too terrible. As a plus, you can attack on this screen. Upon entering either the building or the sewer, the actual game begins. It is a regular side scroller, but depending on which turtle you have the enemies are either hard to hit, practically impossible, or actually impossible. In my opinion, Leonardo is the best character, so you'll want to use the other guys first. You get to use all four as your sub-continues, and then there are continues.
Most of the game play is repetitious, but they do try to mix it up with frequent boss battles, and even more frequent sub-boss battles. The boss battles are difficult, but the sub-boss battles are pretty easy. The biggest complaint I have is on the second level where you need to swim in between electric seaweed. This part is practically impossible, and I've only completed it a few times to date, even with the large amount of time I've put into it. After that, it's just more of the old stuff, and I never got too much farther than that.
The music is some of the better music I've heard in some of these games; but it's not spectacular. The backgrounds are pretty god, but again, nothing to write home about.
In all, I would definitely recommend getting this game if you are a fan of the turtles, but I wouldn't actually play it that much. I'd get the later ones and play them a lot more.