I picked it up yesterday, got the last copy they had. Its pretty good, it isn't spectacular. It can't even touch Virtua Fighter 4: Evolution, but its a good game nonetheless. The online play (via Xbox Live) runs incredibly smooth and lag-free.
The new "Konquest" mode (Mortal Kombat RPG, basically) sucks total ass, it has some of the worst graphics I've ever seen on consoles of this generation, it looks exactly like a Nintendo 64 game. "Konquest" mode is basically a big tutorial for the game, disguised as something new. It consists of a bunch of "Go from point A to Point B and talk to a person and/or grab [insert item/artifact/Kamidogu here] and bring it back" type missions, where you can gain "Koins" to spend in the "Krypt" to unlock new characters, outfits, stages, movies, artwork, pictures, and etc. After some missions the person you are working for (basically a MK character) will train your character in their particular style of martial arts.
The Kamidogu are some sort of ancient artifacts that have some special powers or something, that the Elder Gods can use to fight evil in the world. After you collect the Kamidogu in each world (Earthrealm, Netherrealm, Chaosrealm, etc) you will return to the "Nexus" (a series of portals to other realms), to move on to the next Kamidogu to collect. What really sucks about Konquest mode, is that you HAVE to play through it if you want to unlock all the characters/stages. You can gather keys in Konquest mode which unlock special tombstones in the "Krypt", which contain the characters/stages/costumes/etc.
IGN Xbox's Review of Mortal Kombat: Deception (8.8/10)
GameSpot's Review of Mortal Kombat: Deception (8.5/10)
For Mortal Kombat fans, you'd love this game. For fighting game purists, stick with Soul Calibur II, Virtua Fighter 4, and/or Guilty Gear X2 #Reload.
I'd give the game a 7.5/10.