While MLB isn't the greatest PSP game in the market, it is easily the best sports game for the system.
Batting is like a mixture of MVP, and ESPN. It has the same "move control stock" method as ESPN, and has the same "move D-pad" method as MVP. The problem with this is that it makes it too much of a guessing game, and takes away alot of the fun, even with the "Guess Pitch" turned on.
On easy mode, the game forgoes the ESPN style and goes with MVP's only. This makes the game much easier, but still dosn't give you the feel of control.
Pitching is where this game's at. It's just like MVP's, but better. You have a batting aimer that goes up and down. Up is the power of the pitch, and down is for the accuracy of the pitch. The problem with MVP's is that if you have the bases loaded, the pitcher dosn't get that nervous. In MLB, if you have even 1 man on base, the pitcher gets really nervous, and the pitching meter gets REALLY fast. This makes this game easily one of the most tense baseball games I've ever played, and makes this game fun, even in extended periods of play.
The Graphics are great for a portable game. The detail in the player models and stadiums even match it's big brother (MLB 2006 for PS2), but aliasing problems are a problem, but very little slowdown.
The Sound is also exceptionally great for a portable title. The Play-by-play commentary is awesome with plenty of tracks of commentary. The 2nd guy gets really repetitive after awhile, but besides that no complaints from me.
Even with it's lack of a Franchise mode (it still has a season mode) or replays, the game is still astonishally great, especially for a portable title.
The season mode is more than enough for most gamers, and the replays have always been a hinderance to me, anyway.