I have it, and I also think it is great. Like StealthTH said, there is no live video. Live Audio (your choice of home or away streams) as well as video highlights, live box scores, and play-by-play are available. The cool thing about the video highlights is that there is not much of a lag at all between the action happening and the highlight being posted. If there is a home run or some other notable play, it will be available to view in no time at all.
I drive home from work every day listening to a ballgame. Every once in a while the app has a problem connecting to the stream, but I just kill the app and toggle Airplane Mode on and off again to reset the 3g and then the app is able to connect again.
One word of warning - I plug my Moment in to my car stereo's auxiliary port, and I have to turn my stereo volume way up to hear the ballgames (not the case when I listen to Pandora or mp3s on my sd card, so I think it's the At-Bat app to blame). So remember to turn the volume back down before you get out of the car, or else the next morning you will blast your eardrums.