The Graphics, The Sound, and The Gameplay
Part of the reason for that is because the weapons that you have in the game feel powerful, like weapons should. You have the standard fare of guns to play around with, including a pistol, submachine gun, assault rifle, shotgun, and rocket launcher. There's also a scoped, burst-firing rifle that's a dead ringer for the Master Chief's battle rifle in Halo 2; an incredibly nasty particle weapon that sears the flesh off of opponents; and a few other special toys. All of these weapons, even the pistols, pack an incredibly satisfying punch and are capable of putting down opponents quickly (you can even dual-wield the pistols, for that extra John Woo-style gunfight action). This goes against the genre's convention, since most shooters usually scale weapons on a curve, with the smaller and lighter ones being next to useless later on in the game. That's not the case in F.E.A.R., and virtually every gun you use can tear up the place.