I'm fine with how April, Meat Sweats, Leo and Mikey look. Donnie, Raph, Splinter and Draxum look a little too weird.
I actually have somewhat mixed feelings on Splinter to be honest. I like that he's back to being short and grey. However, I don't like the flat face and I don't get why he's fat, did they want to combine him with the ancient one? It does kinda look like a mash-up of the two.
And I'm not really a fan of the top knot returning from the PD movies. Same issue I have with Raph and Don, I don't want to be reminded of OotS.