I wish there was an option between mediocre and abysmal.
As for me, I thought it was the most boring of the NRS Mortal Kombat games. Though I wouldn't necessarily label myself a lab monster, I really enjoy spending time training to figure out new combos and setups and weird things, and I felt there wasn't really much of that in this game. To me, the game really felt like it played itself. By that I mean it felt like every part of the fighting (particularly the combos) were designed to be played a certain way and that was it. I never felt like I was discovering something or playing my way, I was just doing what my characters were designed to do.
The game was also clearly rushed, and I'm 100% with Tom when saying that it's VERY incomplete. It's better now than at launch, but it still feels very shallow. The custom moves and their slots were just so poorly handled that it makes me sad thinking about it. I'm also really annoyed by NRS's patching choices with this game. Their patching of characters was very strange with certain characters like Jacqui consistently getting away with murder while others were smacked down much harder. I despise Fatal Blows, and I'm shocked that they never "fixed" them. Although I like the gear, I hate how long it takes to get what I want; I would honestly rather just have costumes instead of grinding for pieces. I also strongly dislike how characters can have useless or near-useless armor breakers. Seems like such a poorly-thought-out and tacked-on mechanic. Also, the music and general design of the game is just too superhero for me, especially the menus. I know that sounds like a nitpick, but just looking at the menus turns me off where in other MK games (pre MKX), looking at the menus would always get me hyped. I also think that their super slow DLC rollout with some characters that people pre-ordered before the game coming out taking around a year to be released will leave a bad taste in a lot of mouths. Last big complaint here is that Towers of Time are AWFUL and I hate them. NRS got it right with MK9's big tower, and have failed ever since by treating it like a mobile game.
As far as good, I think the roster is one of the best in the series. The graphics also look great, and the netcode is very good. I also really like how much competitive MK there is to watch, but I just wish it was more enjoyable to spectate. Storymode looks nice, but it's all nonsense, and I'm glad this MK9 reboot era is (probably) over now. I really think NRS exceeds with all the little bells and whistles of the game. For example, I love all the intros, taunts, outros, voice lines, and all the other little quirks that most games don't/can't incorporate. They just really nail the presentation.
Anyway, I do like it more than X, but I think that NRS just went too far trying to make it balanced to the point that the game just feels so shallow and boring. I believe the main culprit is NRS's desire to make each game different from the last. Coming up with a nearly completely new game every two years that's super fun and super balanced is just too monumental a task. I like it more than MKX, but less than MK9. Hopefully once NRS is done with their Marvel game, they can get a nice long development period to produce a truly fantastic MK12 game using all they learned from this trilogy. Ultimately, I think its legacy will be akin to other unfinished games where people see it as a game with tons of unmet potential that just bit off more than it could chew and caused a lot of unrest in the community.