Question about PSP's and it's games..

So, recently i've been thinking about buying a PSP. I've been doing my comparisons and overall i'd go with the 3000 over the GO for a number of different reasons. Anyway, how are the games for the PSP? What I mean is, do all the games have the same features as a game for the playstation 3 would? For example, you can buy MLB 10: The Show for both systems. I've heard that that the PSP version is a bit dumbed down from the PS3 version and some features are not included. Now, being that it's a sports game, this doesn't matter to me much. But, if I were playing a game that has an single player mode with a main story, I'd want to have the same exact features as the PS3 version. Can anyone clarify this for me? Thanks, this will help me out a lot when I make my final decision to buy a PSP or not..

PSP TOP 10 OF ALL TIME:
1.Metal Gear Solid: Peace Walker
2.God Of War: Ghost Of Sparta
3.Resistance Retribution
4.Monster Hunter Freedom Unite
5.Socom Fire Team Bravo 3
6.GTA: Vice City Stories
7.GTA: Liberty City Stories
8.GTA: Chinatown Wars
9.Test Drive Unlimited
10.Dungeon Siege Throne Of Agony

^this are the games you need to have.

ModNation Racers ported well. You can expect some degradation when dropping from a blu-ray drive to a handheld, but every port I've played runs fantastic. Really just depends on where you'd prefer to play any given particular genre of game. Racers, puzzle games are perfect for on-the-go gaming. Deep immersive Peace-Walker-ish adventures are best left for the La-Z-Boy.