The new game modes don't make up for the same old boring kombat.
Mortal Kombat: Deadly Alliance was released to pretty good reviews and decent sales. So it's not surprising that Mortal Kombat: Deception doesn't mess with MK:DA's successful formula too much. Rather, Deception adds onto what Dark Alliance began by introducing a host of new game types, characters, and a very long quest mode.
I didn't like MK:DA's fighting. It was stiff, shallow, and generally not fun. Deception retains the same fighting engine, but it does make a couple of improvements. The first change is the introduction of combo breakers that you can use a few times a fight to stop your enemies attacks. Also new is a gauge that shows you when your enemy is vulnerable to counter attacks, when he's blocking, and when he's attacking. The biggest change is the "danger zones" in each arena. At any point during the fight, you can instantly wipe out your opponent by hitting them into one of these. There's a pit of fire, a grinder, a cliff, and some floors that you can be knocked through. Sometimes getting hit into one of these feels cheap, but it is actually a fun element to the game when you're playing with a friend. Even with these changes, the battles are generally the same as MK:DA, and grow tiresome after a few hours of play.
Like MK:DA, Deception has a ton of content. Some of it is pretty good. Most of it is really worthless. Konquest mode has been completely overhauled. It plays more like an RPG now than a set of missions. You'll interact with every MK fighter, collect a lot of coins, and fight across a host of different realms. Konquest is necessary to unlock the strongest fighter in the game, but it's never especially fun to play. Also added is a MK-themed chess game. It plays basically like chess, with a few twists ,and you'll need to fight to take a space occupied by an opponent. This is totally unneccessary, and not that much fun at all. Lastly, a tetris-like puzzle game is the best of the new games, and is a blast. It's a combat style puzzle game where you'll try to clear out your board before your enemy. It's a great diversion from the main game. The krypt returns, basically unchanged, and still holds a ton of unlockable content.
Deception retains the same combat from Mortal Kombat:Dark Alliance, and adds enough new features to separate it from MK:DA. However, the stiff and shallow combat has not been addressed, and the new features are very hit-or-miss. I would suggest this game as a rental, or a bargain bin purchase.