Overall MLB 2K9 is a definite improvement over MLB 2K8, yet there are still issues that need to be addressed. Once they have been addressed and subsequently fixed then this will be a tremendous baseball title. As it stands right now it is a fun title to play with your friends but it isn't living up to its full potential. If you are a baseball fan Totally360 would definitely recommend giving this game a try though.
There is a free demo on Xbox Live for everyone to try and see what they think. If you like it then by all means pick the title up at your local game store. It should definitely be interesting to see how the game evolves as the regular baseball season starts up and evolves.