A great game, until it suddenly isn't.
Syphon Filter starts out on a good foot, with a fairly engaging single player campaign. It has decent graphics, decent sound, decent gameplay, and what appears to be a great multiplayer setup.
But that's just the surface.
Once you beat this game, you will begin to hate it. The multiplayer is good, but the ranking system is among the most awful I have ever seen. If you didn't buy the game in the first week, good luck, because everyone but you will have AK-47's and rocket launchers while you are stuck with a garbage can assault rifle. It takes months to get to the point where you can be competitive in this game.
Further compounding the issue is how lame the single player is the second time through. The extremely linear campaign is no fun the second time at all.
If its a weekend playthrough, or you live in your mother's house and have time to blow on this game, you will love it. For anyone else, look elsewhere. The PSP still doesn't have a good shooter.