This is actually a great game, how come no one likes it?
The Turtles do actually handle differently from one another. Some turtles are faster, some have better range, and for some reason some turtles are a better fit for some boos fights. Out of the bunch Leo is the most well rounded of the bunch to go the game alone, he has great range and is fairly fast. Michey fells like he hits faster and runs faster, the same goes for Raphael. Donny has the best range but is the slowest of the group. Depending on what you need for the game you will find a turtle that will suit you best.
The achievements are fun and challenging to get. Some are easy; get flattened, get zapped, beat the game, etc. Others will take time and skill to get such as beating survival at least on normal, beat the game using every turtle, kill 5 enemies at once with an explosive object, etc. You can get all the achievements, I just earned the rest I needed this morning. The survival achievement is probably the hardest to get, but the more you play the better you get and this achievement will soon be cake for you.
The game is not perfect I'll admit, every once and awhile you're character won't move or attack even though you are hittng the buttons. Some bosses are cheap but once you figure them out they're easy. There isn't any cuts scenes (besides the beginning and ending cut scene) or anything to really move the story along or show the turtles personality. The game is quick but there is a lot of replay value here, I played the game probably more than 10 times. You can forgive most of these issues and enjoy the game for what it is, an awesome beat em' up with a lot of replay value and a sense that you are really kicking some shell.