I kind of love the F.E.A.R. franchise, if only because the games are very challenging but addictive in terms of their overall design. Perseus Mandate is a separate expansion with a new character, so it's a little bit different in overall design from F.E.A.R. and F.E.A.R. Extraction. F.E.A.R. Extraction picked up where the first game left off, whereas this one sees the game from the viewpoint of a different character.
If you play this game on extreme difficulty, you can expect to get very frustrated, but it's still so much fun that it almost doesn't matter. Basically you move from checkpoint to checkpoint clearing rooms of enemies with some "nightmare" segments that act as breathers in between. This game has a ton of enemy types and is actually overall probably the hardest game in the franchise.
There is one particular enemy type that has way too much health and is very difficult to kill. This game also adds more weapons, including a really cool gun that shoots an electrical arc and obliterates enemies with ragdoll effects. For an old game it still looks pretty good, but it's not as polished as the F.E.A.R. base game. You can still slow down time, but sometimes this doesn't even matter because enemies can one shot kill you on the hardest difficulty. For some reason it's extremely satisfying to survey a room of unaware enemies, slow down time and quickly pick them off. If the enemies know your position, you really need to listen carefully to the audio to determine how many are left or how far they are from you. I really like how the audio plays a significant factor in the game play and it makes F.E.A.R. one of my favorite first person shooters.
While the story isn't great (What FPS story is? Halo maybe) it is nice that there's a cohesion between all three games. The developers clearly tried to make sure all the story pieces and characters fit together so it's not like this game goes completely off the rails with storytelling. This game isn't very long, but like I said if you play on the hardest difficulty you can expect to replay segments several times as enemies will obliterate you in seconds. It's totally unfair but that's what makes it fun. The fact that the odds are so strongly stacked against you gets you into the zone where you start playing really well to succeed because you have no choice.
I recommend playing all five F.E.A.R. games because they are great. While this one is not the best it is definitely a great game, and it ends with more of a climax than the original F.E.A.R. and actually has a boss fight of sorts.