I rented this game with low expectations and--even at that--I was disappointed.
It's entirely possible that I was playing the game incorrectly and/or that you have to tweak the sliders to have the game make sense, but this was my experience (on normal difficulty):
There is absolutely no rhythm to the pitching motion controls and unless there's something I'm not understanding about the game of baseball itself, the pitcher fatigue is completely absurd. Your pitcher ends up at like 50% stamina after one inning. Also, the effects of fatigue seem inconsistent. One pitch you'll have a relatively hard time throwing an accurate fastball, and the next pitch it'll be ridiculously easy. Actually, pitching is ridiculously easy, control-wise, all the time. It's very easy to get the ball exactly where you or your catcher wants it. But that didn't stop me from giving up 8 runs in 4 innings because of home runs. I threw exactly where my catcher told me to with a good amount of accuracy and with the recommended pitch type but it was still out of the park.
Oh, and I went through 3 pitchers in 4 innings. Not because I wanted to switch it up, but because of injuries. I'm not a baseball expert, but a pitcher should be able to last longer than 2 innings.
Unless I missed something terribly important in the instruction manual, fielding is a joke. Your players don't move well and they miss easy catches. The throwing is pretty much broken. If your shortstop catches a ground ball and doesn't have a hard time handling it, you'd think you'd be able to throw out the runner going to 1st. Not in 2K9.
On the other side of the ball, hitting is terribly difficult. You have to use the control stick to pick a spot in your strike zone to swing at and you have to time your swing perfectly. That plus you have to keep your eye on the ball to tell if it's even going to be worth swinging at.
The sound in the game seems pretty good and the graphics in the game didn't strike me to be as ugly as reputed to be. Until there was a close-up on a player's face. None of the players look good. I don't know what happened to 2K Sports games' graphics. They seem to get worse every year. I swear NHL 2K5 for PS2 looks better than NHL 2K9 for 360.
If you want a baseball game for Wii, don't bother with this one. Wii Sports Baseball is honestly a lot better.