Another big question for me is which version to get? The PS3 version has Kratos, and that is an unbelievably awesome edtion to Mortal Kombat lineup. The Xbox character has not been announced, leading to speculation that there simply isn't a 360 unique character. Instead, they'll get the 2 initial DLC characters for free. Such a missed opportunity for a Gears character

Anyway, onto the game.
1-4 Players (offline)
2+ (online)
2 (local) vs. 2 (online)
720p, 1080p - 60fps (frames per second)
X-Ray moves
2 fatality minimum per character
stage fatalities
Kombat Kodes - In multiplayer matches, during the 'versus screen'; by pressing the attack-buttons you can cycle through symbols for each square. Player 1 can change the first 3, Player 2 changes the other 3. Inputting a code, unlocks modifiers during that fight: like multi-colored blood, zombie-looking characters, armless characters, and so on.
Single player
Ladder
Story
Challenge Tower
Tag Ladder
Training
Tutorial
Practice
Tag Practice
Fatality Training
Test your Luck
Test your Might
Test your Sight
Test your Strike
multiplayer
Versus mode (2/3/4 players)
Team Ladder
Test your Luck - Awesome new addition. A slot machine randoms a series of game modes that effect the match, like no kicking, or triple dmg. Crazy stuff here.
25 Characters right out of the box, with more unlockable (exact number has not been reviled). +1 if you get the PS3 version for Kratos. There will be 2 characters available as DLC soon after release.
25 Stages right out of the box, with others rumored as unlocks. Several of these stages have day and night versions/cycles.
You earn "Kombat points" that can unlock all sorts of shit, from costumes to classic soundtracks.
I even glossed over a bunch of smaller stuff. The game seems suitably epic IMO and they'll get my "Day 1" money.
Here's a fun little video that briefly touches on several of the game's features:
http://www.youtube.com/watch?v=RGVLWE4ly3Y