I fully reviewed this game at:
Mortal Kombat 9 is definitely not the best in the series. The best 2D MK was probably Mortal Kombat 3 - but, that game had so much content: bablities, friendships,etc - it got ridiculous. The fighting was awesome though and that game introduced plenty of awesome characters such as KABAL, cyber ninjas and the Mark Fuhrman-like STRYKER. the best 3D MK was arguably Armageddon thanks to it's long list of characters and 3D style, but, I think my favorite was MK: TRILOGY on Playstation since it combined all the characters in a 2D space.
Mortal Kombat's singleplayer is fun and has plenty of Jaw dropping moments, secret character alterations and incredible sound and gore. Unfortunately, the experience is horribly balanced. Bosses cheat with impunity and you are often forced to fight tag teams with no partner of your own. Near the end of the game, you need to fight dual endurance matches against 3 opponents and then fight Shao Kahn who's difficulty level is ridiculous.
The online experience is not as good as that in MKvs.DCU. I played over 3000 rounds of MKvs.DCU and enjoyed all of them with the exception of those with cheating opponents who spammed "infinites". In this game, just logging in and connecting to an opponent is a chore. something is wrong with this game's online code. It's laggy and incoherent most of the time. To make matters worse, you'll need to enter a redemption code just to download a component in order to get online - a move made to keep people from trading the game in early.
I've beaten the game (twice) and unlocked two hidden characters. Unfortunately, this game is a waste of my $65 and I would trade it in if I didn't know I was going to lose a large percentage of my money. Mk vs. DCU didn't have the gore, but it was a much better effort.