Medal of Honor Heroes had a nice online, but no one ever played it. 32 players, and you could download a small program for setting up your own host server on your PC. I thought it was a neat, innovative use of the PSP online features - but like I said, no one ever played, even in the first few days. It's a shame, too, because MOH Heroes isn't a bad game at all. It's short (really short, like 4 hours short), but it has a nice compliment of options for a PSP FPS. Auto-centering worked great. As far as WWII FPS PSP games go, it's the best of the three out there. Brothers in Arms is fucking awful, and COD: Roads to Victory is pretty but disappointing. When it hits the bargain bin I recommend it. You can set up bot deathmatches for quick play, and the bots are pretty good.
Overall, though, I'm over FPS on PSP. Just won't ever work to anyone's complete satisfaction. They should make a good 3rd person COD, BIA, or MOH game instead.