They are, in my opinion, the worst iteration of the TMNT. The show reminds me of Ninjago, in that it tried to be "edgy" and "lore-heavy" while still dumbing everything down for kids. I didn't like Teen April or her romance with Donatello, Casey Jones was unnecessarily stupid, most of the voices are annoying, and its crossover with the 1987 series, while not as badly as Turtles Forever, greatly disrespected the 1987 Turtles and downplayed their ability, portraying the original show as a cross between He-Man and Barney. It was one of the first huge Nicktoons to be a reboot of some sort, which, while inevitable, still set a sour precedent, as like 80% of the upcoming Nicktoons are reboots or adaptations. A large amount of the TMNT fanbase these days is tweens who grew up with the 2012 series and blindly defend it and trash all other iterations without so much as watching/reading them, showing that they're either blinded by nostalgia or just immature. Also, one of the biggest things about the show that annoyed me on the regular was that the characters always referred to each other as "Donnie," "Raph," "Leo," and "Mikey." I've always thought that those nicknames were unnecessary and annoying, and to call them that ALL THE TIME really grates on my nerves.
They had some cool LEGO sets, though.