Insofar as it has a main character, that main character is April O'Neil (Megan Fox), a news reporter yearning to break into something better than idiotic puff pieces that require her to demonstrate some faddish exercise regimen by bouncing up and down on a trampoline, a task that Fox is considerably better suited for than she is at playing a passionate crusading journalist. Though in this particular case, presumably to cut down on effects costs, the turtles aren't themselves the collective protagonist of the film.
TMNT '14, which I gather is roughly to the 2003-'09 animated TV series as the 1990 movie was to the 1987-'96 animated TV series, provides a brand new origin story for the famous chelonian supeheroes, living in the sewers beneath New York City and training in the art of ninjutsu under the guidance of their adopted father, the mutant rate Splinter (acted for motion capture by Danny Woodburn, voiced by Tony Shalhoub). Though my old friend "execrable" put up a good fight. "Revulsive" is the one I like best, after a quick trip to the thesaurus. And when a man with neither style nor talent attempts to slavishly copy from the Michael Bay Playbook, as we're seeing here, the results are so dire that we need new vocabulary words to describe them.
Other than that producer Michael Bay, bless him, is a stylist with a good eye, if nothing else and director Jonathan Liebseman is not. There's no sane reason for Teenage Mutant Ninja Turtles to be as bad as it is.