heres my opinion
from a moveset point of view: MMH, not because he has a teleport, thats canon and fits well, but when i see MMH hes normally all about shape shifting and phasing through stuff, which you dont really see in his move set. I thought it'd be awesome if his trait had something to with phasing, like he'd become projectile invincible for a certain amount of time, or something like that. I feel like he should have some sort of special or normal where he goes into a different shape or something. they had plenty of potential and i feel they didnt abuse it enough.
from a overall character point of view: nightwing, i know hes my main but trust me im not being biased, im sure everyone will agree with me on this if they know anything about the character. hes an ACROBAT, even more acrobatic than batman and dare i say catwoman, he should have a double jump, or a grapple similar to cyborgs, a faster walk speed or SOMETHING. Seriously, i wouldn't be surprised if nightwing in staff stance has the slowest walk speed in the game. to be good with nightwing, u have to be patient and choose your openings, i feel as if he should be a fast paced rushdown mixup heavy character (similar to spiderman in umvc3, u play as him and he actually feels like spiderman) i just dont get that same vibe from nightwing.
as far as looks: raven.... i mean WTF!? i know NRS is famous for not having the prettiest females, nor do i believe raven should be good looking at all, but if u ask me she looks NOTHING like any of her previous interations. the closest they came was with the teen titans skin and that barely looks like the raven i remember, all they really gave her was the same color cloak and skin. i mean shes hideous, absolutely ugly lol
other characters..
cyborg, could've had more tools, hes a cyborg for christ sake, he has like 2 moves.. he should have like 20.
ares... the god of war.. he could've had more things to utilize, i mean for the god of war you would think he would have more than just a sword and an axe right?
green arrow.. this is probably just a personal thing but i totally thought he was going to be a complete zoning character. that wasnt the case