Not many changes, but a lot of tweaks to the game make it much more enjoyable
Now I have bought 08, 09, and now 10 and i honestly believe that '10 is the best one yet. Everything has been tweaked in the new game. I like the fact that you can choose if you want to use the new analog controls for base running, in road to the show, or the old button layout. I hated the "new" base running in the previous game. The graphics look a little better then 09, not much, but its still an improvement. You can also customize your created character much more in 10. You can choose what color your players gloves are, your wristbands, your shoes, your catcher gear, and other things. Its a minor addition, but i still like it.
The difficulty of 09 is what turned many people away and its really not as hard in 10. I remember when i made my character in 09 it was ridiculously hard just to get him to a .250 average, but in 10 im able to stay around .300 most of the time. I do disagree with the gamespot review where they said that it had long load times because the load times are the same as they were in the previous games.
I thoroughly enjoyed mlb the show 10 because even though it didnt add anything new to the series, it did end up being the most polished game in the series. If you want something revolutionary you should probably get a different game, but if you just want a great baseball game then this is the one for you.