A great addition to your PSP collection, Socom is worth the money.
The graphics in Fireteam Bravo are great for a hand held game, but could still use improvement. As with most games, you can find a few noticeable graphical glitches but nothing that detracts from the game.
The PSP only has one analog stick which definitely changes the gameplay. For example, now, using the 'R' Button let's you lock on to an enemy. However, it's not just lock and shoot with every weapon. As in real life, rapid fire guns would have less precision then say, a sniper. So if you're locked on to a guy and have a sniper equipped, you'll have a better chance of nailing your target. If you had a pistol out on the other hand, you'd need to get closer to guarantee a good shot.
The main complaint I have for Fireteam Bravo is that it's pretty tough to see around corners, adjust your camera, and get a good angle on your enemy. This is mostly because you're always looking straight ahead. And the only time you're not looking straight ahead is when you have free look on, but then you can't move and must stay stationary. This would be very difficult to solve without having a second analog stick though, an improvement someone should suggest to Sony when they announce a PSP2 in the works ;).
Overall, this is one of the few games I can honestly say are worth getting for the PSP right now. If you've got a PSP, definately pick this game up. If you don't have a PSP, don't pick it up just for this game. (And wait for it to go down in price, $150 would be more like it)
As a final note, the M (Mature) rating on this game is obviously something to watch out for but seems over stressed. This game is blood free but does have some explicit language at times. Keep your eyes open, but you should be fine with this game.