F.E.A.R Files is awesome and it answers questions from the first game.
Extraction Point: This expansion takes place directly where the first game left off and in my opinion is the best out of the two. There are only 3 new weapons but there pretty cool to use. Still just like F.E.A.R Extraction Point doesn't have any more horror and is still a very bloody fps. The story is very good and easy to understand and follow.
Perseus Mandate: This expansion takes place in between the original F.E.A.R and Extraction Point so this is definitely the game to play second because if you play this first the story will be a little difficult to follow. The thing I liked most with this pack is for once you get a little help and not just on your own through the whole game because you're playing as a different F.E.A.R team instead of the Point Man. This expansion has a little more horror than Extraction Point but not by much. This expansion is also a little more of a challenge with more difficult enemies but you get stronger guns which is really cool and helpful.
Overall both expansions are a good length but I only recommend this for fans of F.E.A.R because this adds more to the story if you didn't play F.E.A.R you should definitely play that first or you won't understand the packs as much.