Not scary at all, but it's a spectacular, adrenaline pumping carnage.
However, it has best shoot outs in the series; explosions and other combat effects are made very well, AI is above current standards and most weapons are fun to use (Not to look at, sadly, they resemble more of NERF toys, than actual firearms. Like i wrote, consolized).
The game itself is decently ported, it runs smoothly on almost anything bought in the last 3 years and keyboard/mouse controls are just ok (remember, playing fps on pc with a gamepad is a criminal offence in some countries, or at least it should be).
It has some atmosphere, which feels true to the series, but it's hardly unsettling, leave alone terrifying. But FEAR was never about being particularly scary, it was about shooting your way thru dozens of foes, sometimes interrupted by some supernatural, irritating bull***t jumping at your face. There's slightly less of aforementioned jumping bull***t in FEAR 3, but for me it's a good thing. It is always better, if a game does not try to make me s**t my pants, than the other way around. And I can only think with sympathy about people, who would argue with that simple truth.