Just to get this out of the way, I grew up with the original cartoons and movie trilogy (the 3rd one is really bad, but the first two are pretty good for what they were). And as a reboot/adaptation, there will be comparisons. Now onto the review.
If I go too in depth here, it will take forever. So;
Good Points:
The Turtles themselves, overall, were actually okay. Michaelangelo being a horndog for Megan O'Neil is kind of creepy. Why? Turtle. Penis. And was there really a reason for Donatello to NEED glasses? I know he's the smart one, but do you need glasses to be smart?
Really that's about it for the good.
Bad Points:
Megan O'Neil. All Megan Fox has going for her is her looks. I'm sure she's a nice person and all, but she cannot act at all. Would have been better with an actress who can actually act.
I know I said the Turtles were, overall, good. But being 6ft tall, roided out, bulletproof, and super strong. Why do they need to learn ninjutsu? SOMEONE obviously did not think that through.
Splinter. He looks butt ugly and worse than previous incarnations and has no connection at all to Shredder prior to the movie. Which brings me to my next point.
The origins story. Splinter and the turtles were just lab animals in Megan O'Neil's father's lab. And were "saved" when Megan got them out of their cages and dropped down the sewers. Also, instead of Splinter being a ninja turned rat or at least being an intelligent rat pet of a highly renowned ninja, he finds a book on ninjutsu in the sewers, somehow masters it in relatively short time, and turns around and teaches the turtles.
Also, Splinter is more of a dick in this film than in any previous version.
The villains "evil plot" is ripped directly from The Amazing Spiderman. Seriously, it's pretty ridiculous.
Shredder, in his "Shredder outfit" looks more like a discount Megatron than Shredder. Probably because short of wheels, he may as well be a transformer.
Finally, this film isn't even really about the turtles, it's about Megan O'Neil. The Turtles are more like her sidekicks than anything, especially considering it's 30 minutes before we even get out first look at them.
Overall, I give this movie a 4/10. It's bad. The Turtles are okay and the bright spot of the film, but there's not enough of them in it to make it better. It's something kids would probably like, but the original TMNT movie from 1990, while no 5 star movie, covers it's bases much better and the acting and storyline is also a lot better.