I have to say that I'm still shocked when people compare the PS2 game with the PSP game. The PSP is not meant to be an equivalent experience and of course sitting on your sofa and playing on a large tv is always going to be better. But for those of us who are on the go (me on planes often), the PSP has been a godsend. At 1st the games were mostly poor ports of the console versions, but lately, the little unit has come into it's own. I recently flew from NY to Los Angeles and played GTA: LCS, Syphon Filter and MLB: The Show (American baseball) - all fantastic games. So the PSP is a winner for me and continues to get better.
As for the Pro Evo PSP game itself, I have to say that I'm highly disappointed. Small screen and less buttons aside, Konami really dropped the ball here. Only two generic stadiums (MLB: The Show has all 30 Major League stadiums, plus 3 minor leagues full of teams and stadia). No ML (MLB: The Show has a career mode). Very limited camera angle which makes the button limits worse. Only Ad Hoc (psp to psp) multiplayer (MLB: The Show has Ad Hoc as well as infrastucture mode).
There is no excuse for Konami not to iclude all the bells and whistles on the next PSP game. If MLB and Madden football here in the States can do it, then certainly so can Konami with soccer.
As for this Pro Evo PSP version, stay away. There are so many more excelent games worth playing on the system.