I don't care one way or the other about Megan Fox as an actress--I've seen maybe two of her roles so I'm largely indifferent to her as an actress--but put the proper appearance to an established character role, okay? Megan Fox does not look like April O'Neil. It's like how Noah Ringer was cast as Aang in The Last Airbender, and it didn't go over with that fandom.
The only way they can really make this white guy work as the Shredder is by revealing that it's a shell body for an Utrom, much like how they did the first Shredder in the 2003 cartoon--and even then they had the decency to A) have the shell appear as an Asian man, and reveal that said Asian body was deliberately based off of the original Shredder of that timeline, an Asian who bonded with a demon to become the Shredder.
The TMNT movies entertained the usage of Utroms before--they were in fact going to have Professor Jordan Perry reveal himself to be an Utrom in the script of the second movie, but decided against it because too many people were unfamiliar with the Utroms from the original comics, and figured they'd mistake him for 1988 cartoon's Krang, but given the success of the new cartoon and its usage of Utroms, they've lost that excuse.
But honestly? I just don't see them going down that road. So we're stuck with white guy!Shredder, and I don't know how well that's going to go over with the rest of the fans. It sure as hell isn't going over real well with me, after all.
A lot of people have issue with the turtles' facial designs, and I can mostly understand it, but for the most part I'm okay with that. A lot of people take issue with their having lips, but I can understand that design choice if nothing else. Lips help with expressions and emotions. The rest of the body I'm okay with, it's hardly the first time the turtles' have changed up their attire in the franchise. It's the human characters that the production team dropped the ball with.