The basic combat system is totally competent and fun. It feels like a Platinum action game; tight, responsive, with the usual slew of Platinum's mechanics and a few new twists. Like Korra it's a little on the mashy side, but totally enjoyable. The new Parry system is probably the highlight; I think you could really dominate if you got a feel for it. If you dumped one of the Ninja Turtles straight into any other Platinum game you'd have a great time.
Unfortunately, the game itself just doesn't hold up its end of the bargain. Imagine trying to play Revengeance, but there are three AI controlled Raidens running around at all times getting in the way, filling the screen with particle effects, and looking pretty much exactly like your Raiden so you regularly lose track of which one you're playing as. There's no way to play as a single turtle; the best you can do is tell them to 'Wait', which just makes them slightly less aggressive, but they'll still fight alongside you. On the rare occasion you get a few moments to yourself, it becomes clear that the game is balanced around having four turtles mashing away at once, because your individual damage output is pretty low.
Mission design and bosses are genuinely trash. Imagine Korra's empty corridors, only instead of just fighting enemies you're doing awful co-op bullshit like slowly carrying a heavy object to a waypoint while your buddies protect you from waves of guys, or holding Circle on an interactable object until a timer ticks down while your buddies protect you from waves of guys. Maybe all four of you will protect a thing from waves of guys, just to spice things up. Bosses are just big damage sponges that hit hard, and when they get to low health they get super aggressive. Forget phases, interesting attack patterns, any other Platinum-ness. Your AI buddies are terrible during these fights, and you only get three Continues per level. Lose them all and you have to start the level all over again.
Anyway, I'm going to drop the difficulty to Easy and at least finish the game. Platinum is my favourite dev, so I tried to stay positive even when the messy-looking gameplay videos started coming out, but so far this game is a big disappointment. I fucking loved Transformers, and I think Korra is at least totally decent, but this game is a real stinker so far.
EDIT - Though, I mean, maybe you'd get something more out of it if you played co-op? I'm just not a multiplayer guy, and I don't even have PS+ at the moment so I can't check, but it couldn't be worse.