Both IGN and OXM have placed each of their respective reviews for Mortal Kombat vs. DC Universe on their websites. First, from the IGN review:

However, before we get to the modes this game offers, talking about the fighting system MK vs. DC employs is probably a good idea. When things were 2D on your SEGA Genesis and Super Nintendo, Mortal Kombat was simple: up was jump, down was crouch, and left/right moved you left/right. Being an awesome fighter came down to timing your blocks and moves while dodging ranged attacks the best that you could with your limited movement options. However, when MK made the move to the 3D realm, things got sticky. Suddenly, characters could just walk deeper into the plane and watch Liu Kang's fireballs float past them harmlessly. Mortal Kombat vs. DC Universe blends both of these styles with a varied amount of success.
In the end, a casual fan sucked in by the allure of DC characters will polish off the six-hour story and maybe a few arcade trees before becoming frustrated by their inability to progress through Kombo Challenge and the mode's repetitive nature in general. The characters look good, but there are clipping issues with capes and whips while some of the backgrounds look weak. Meanwhile, hardcore Mortal Kombat fans are going to be saddened by the fact that a lot of the moves look like the ones they've seen before and that Fatalities/Brutalities -- the focal point of any MK game -- have been neutered.

And from the OXM review:

It’s therefore a relief that Mortal Kombat vs. DC Universe has the best pure fighting action of any MK game since Mortal Kombat 3. Gone are the weapons and alternate fighting styles introduced in MK: Deadly Alliance — MK vs. DC Universe goes back to the fighting series’ roots with straightforward kombat, few frills, and well-balanced characters. The absence of M-rated gore is barely noticeable, as the MK cast and DC supervillains can still pull off toned-down Fatalities, while DC heroes can perform “Heroic Brutalities,” most of which still seem pretty fatal, which is what we’d call it when Superman pounds his opponent into the ground like a railroad spike with his fists.
Powered by the Unreal engine, the visuals are excellent. Character models like Jax and Liu Kang border on lifelike, while The Joker and Captain Marvel from DC are realistically stylized. But fans of the last few MK games may be put off by the dearth of extras in MKvsDCU: there are no unlockable costumes or arenas, no mini-games, and only 22 playable characters (including two unlockable bosses) — about a third as many as MK: Armageddon hosted. Online play over Live will enhance this game’s replayability, but a little more content would’ve made it an epic crossover.

Each review covers a fair bit of ground, in the end IGN cites the game as slightly above mediocre, pointing out several flaws in several categories. OXM's review is a bit more positive, with their biggest gripe being the lack of unlockable features.

  • IGN: 7.5
  • OXM: 8.5

To read IGN's review, click here. To read OXM's review, click here. As more reviews from reputable sites become available, we will be sure to make them known here.