3D glasses will make the backgrounds pop out in Mortal Kombat, but the fighters will look the same to everyone.
If you've got the TV to handle it, the PS3 version of the new Mortal Kombat lets you play the game with 3D effects. But don't despair if you want to play some local multiplayer and you don't have enough glasses to go around, as NetherRealm says that the people without them will still be able to play just fine.
According to series co-creator Ed Boon, the trick is actually quite simple. The backgrounds are rendered in 3D, but the fighters aren't. What this means is that if you're wearing 3D glasses, the backgrounds pop out at you, giving a sense of depth, but if you aren't wearing 3D glasses, the backgrounds will look a little blurry and the fighters - which are really the important part, after all - will remain as clear as day. Boon said that NetherRealm didn't want the 3D aspect to complicate anything or to change the basic mechanics of the game, so the 3D mode was essentially cosmetic, allowing you to focus on the fighters a little better, without going making anything difficult for anyone.
It seems though, that a 3D mode for a game like Mortal Kombat couldn't really be anything other than cosmetic. There's not really much opportunity in a 2D fighter to have a lot of objects come out at the player. The exception could have been the x-ray hits, where you see your opponents bones breaking as you strike them, and the fatalities, but it doesn't look like NetherRealm has decided to go in that direction.
A demo for Mortal Kombat, including the 3D effects, comes out for PS Plus subscribers later this week, while the full game comes out for Xbox 360 and PS3 on April 19th.
Source: PlayStation Blog