(Sure, I write a long post and find out I'm not logged in and lose the post.)
Armageddon brings back everyone from all past Mortal Kombat fighting games. Yup, quite a roster. Some are back from the dead. The bosses are all there (though Motaro looks quite different). Even Sareena from a GBA game is there. The joke character Meat from MK4 is there. Chameleon (with a C, from the PSX version of Trilogy, the ninja that cycles through the male ninjas moves) is there for sure, but Khameleon (with a K, from the N64 version of Trilogy, the ninja that cycles through the female ninjas' moves) is probably the ony character whose appearance is questionable. (She really should be, as she has an actual story (that ties into Reptile's), unlike Chameleon.) Plus, there are at least two all-new characters (the heroes of this game's Konquest mode), as well as Kombatants that you can "Kreate".
People shouldn't have given up on the series. I agree that II was the best of the 2D games (that is, until Trilogy, since I love fighting games that bring everyone back, just like Armageddon will). 3 was a step back, 4 was crappy, and the side-story games were kind of embarassing.
But the series came back this generation, and it's a shame if you missed them. Deadly Alliance and Deception were really good. The series showed that it was strong as ever, with actually decent 3D fighting, staying true to its roots, but also new characters, redesigns for all the ninjas (!), and Konquest modes in both games (Konquest in Deadly Alliance had a series of training missions that tried to tell a story, but the Konquest mode in Deception was a truly epic one-player mode).
Since it sounds like you don't know, and it's barely spoilleriffic since it happens at the beginning of Deadly Alliance right in the game intro, is that Liu Kang was killed by being ambushed by Quan Chi and Shang Tsung outside of a tournament.
He came back in Deception rather zombified, though in Konquest mode (since that takes place over a big chunk of Shujinko's life), you can see and fight against Human Liu Kang and Ghost Liu Kang. I wonder if they'll be back and playable in Armageddon (since everyone is back, though not necessarily all forms of them, as I didn't see Human Smoke or Reptilian Reptile). It does seem strange that everyone's been brought back from the dead but they aren't as zombified as Liu Kang. I guess he really likes those chains.
It says October 9, but that's for the PS2 and Xbox versions. A Wii version is coming out Spring 2007.