Medal of Honor: Heroes is proof that the PSP can indeed, do First-Person Shooters. It's a very solid, fluid-playing Game with a solid (albeit short) Single-Player Campaign.
While the control scheme take some getting used to (Analog Nub to Move, Face buttons to look around, D-Pad for various functions, by default), once you get into it, you don't really notice. Think of it as a Reverse WASD configuration, where the WASD is used to Look, instead of Move. Like I said, it's a solid control scheme, but it does take some getting used to, and the look speed is a little slow, even on Max speed. I'll say this: You'll be depending on Iron-Sight and Scope-Shooting a lot in this game, and do to the Control scheme, it's a good bit slower-paced and more tactical than your typical run-and-gun game.
The Graphics are fine by PSP standards. nothing absolutely breath-taking, but it still looks just as good as a PSP game should look. Sound is phenomenal, from the music to the sound effects to the Battle Phrases uttered at random by NPC allies, or Human Allies giving commands in Online Play.
Speaking of Online Play, this is where MoH:H REALLY shines, and sets itself apart from anything else on the system. Boasting the capability for 32-player Online play, and hosted Dedicated Servers with a vast number of Play modes, Characters, Weapons, and Maps, MoH:H is a MUST Purchase for any PSP Gamer who enjoys Online play. It maintains a pretty solid framerate as well, even in 32-player games, which is a major, major achievement for a Handheld Console. The only real issue I can see with the Multiplayer is the lack of Voice Chat(which is a very popular feature in other PSP shooters).
All in All, MOH:H is THE best First-Person Shooter on the PSP, hands down, and one of the best shooters period on the system period. Lack of Voice Chat keeps it from the #1 spot for Online Play, but this is a must-grab for anyone who plans on spending good deal of time playing online.