I'm really late for this review, years late, but I will give you a damn good one.
Anyways, the game is packed with action. it isn't fair to compare this game to Metal Gear Solid, since MGS focuses mostly on stealth based action while Syphon Filter puts you into the role of various secret agents. There are stealth bits in the game, but none of them are fun, which isn't a good thing. They are setup in a way that if you are discovered in any way, you fail the mission. This isn't really that great, but thank God for the checkpoint system. Some missions have optional stealth bits, although sometimes its not even worth it.
The graphics were good for their time, although some may complain about the draw distance, which renders everything more than 20 feet away into black or white fog. This can be troublesome when being shot by enemies that are practically out of sight. The textures can be pixelated in some places, but this IS PSone.
The game controls exactly like the first game, except you can move your agent with the right analog stick, which can be useless sometimes. Also worth noting is the fact that you can now walk. You can't fall off of ledges via walking, and when you need to be precise, this comes in handy. Sometimes you might wish that the manual aiming was a bit smoother, but it works. About manual aiming.. If you are a skilled player, then you should know the fine art of headshotting. Players use this because of the one hit kill and the fact taht you save ammo. Also, some enemies will have flak jackets (body armor) that usually would take forever to kill, but a headshot will quickly down them, and give you their flak jacket. The music in this game is pretty well executed. I love the soundtrack. The music changes in-game, depending on the mood or the situation. If you are undetected and are moving slowly, you will hear a calm steady rhythm, whereas if you are being shot at while you take cover, the music change accordingly. You hear footsteps, characters holding discussions, battles in the distance, rain hitting the streets, cars screeching, lots of things. Good deal.
The game also has a new multiplayer component. 2 players can duke it out in smaller versions of levels from Syphon 1 & 2. You start out with a few characters and levels, but the rest have to be unlocked by doing various things in the story mode. You can play via horizontal or vertical screen mode. Things can get pretty messy and frustrating when playing against a skilled headshot-whore, but you can turn headshots off. Overall this game is pretty good, I recommend it to any action fan who owns a PSone.