F.E.A.R. (First Encounter Assault Recon): Plot Explained
I think it's a lack of depth and ability to think outside the box which have people not understanding the extremely well-written plot of F.E.A.R., so let me explain it simply, which includes some psychological aspects as well, but which is just an excellent plot, regardless, and only enhanced further if you understand the psychology behind what is happening in the game.
Alma, one of two main characters in the game, the other being Paxton Fettle, is your mother, and Paxton Fettle is your brother.
Essentially, the entire plot is this: Alma wants her sons back, and has suffered so much psychologically, that she feels the only way to have them back is through death, that they may be with her. She is a tortured soul, the word "alma" actually meaning soul in Spanish, as not only is her psychic ability something difficult to live with, but not only she was then imprisoned in a secret facility at the age of eight and experimented with due to her powers, but bore two sons who were both taken from her.
She is angry and in pain, and her soul (energy) so strong, that while she may be physically dead, having died at the age of 16 after the birth of her second son (Paxton Fettle), she is able to take physical form and effect the physical world.
You are the first-born son of Alma, being what you hear refered to as "the first time was a failure", which is refering to a secret military group attempting to create a psychic super-soldier.
I believe Paxton Fettle knows and understands this, thus his usage of the super-soldiers which are under his control, is really a method to release and be with his mother.
Hints are dropped by Paxton Fettle throughout the game, such as the haunting whispers of, "You don't know who you are...", and other such chilling lines throughout the game which hint at the fact that you have a deeper and more personal connection to both Alma and Paxton Fettle, which becomes quite obvious as to what that is towards the end of the game.
Alma was the Origin Project, and is the "disaster" you hear refered to in places throughout the game, as the two times she was let out of "the chamber", she killed.
THE BOTTOM LINE: (ALMA) She is a grieving mother suffering from misguided anger and pain, and wants her sons back, of which you are one and the first-born.
THE BOTTOM LINE: (PAXTON FETTLE) He feels his mother, and her "calling" to him, and his entire goal is to set her free and return to her. Along the way, attempting to guide you with him, and make you understand that you're one of the family.
Her appearence in the form of a child is a manifesation of the age at which she was imprisoned, and towards the end of the game, her appearence as an older girl a manifestation of her at the age of sixteen, when she physically died.
The chamber in which she was kept was thought to be able to contain her powers, both when she was alive and when she was dead, but they were quite wrong.
At the end of game, you see Alma climbing up into the helicopter just before the game ends... she is coming for her other son, which is you.
This is a straight-forward run-down of the plot, which hopefully now makes sense to those who could not understand it, and requires you to think and feel a bit deeper, as well as on a more psychological level as well to figure out competently.