I have found it has aged really quite horribly. It felt like quite a fresh game at the time, the graphics were very polished with effects that just looked stunning, AI seemed considered and challenging and the atmosphere was well thought through (although creepy is not the same as scary, this game is creepy). I loved it.
So, last week I decided to reinstall. I got about 40-50 mins in and had to uninstall. It just wasn't doing anything for me, not like when it was the new kid. Having already played through it a few times I didn't expect to be too freaked out, but it did absolutely nothing at all for me. The graphics have aged, the combat was tedious and the "scary" elements I just found quite cheap. I know I would still probably enjoy the later levels, but I couldn't find the patience to get there.
Off the top of my head there is only one game that has ever genuinely scared me. It wasn't through creepy voices or clichéd vague shadowy figures, and unfortunately it only lasts for 15 minutes. That was Half Life 2 Episode 2 (hear me out), fairly early on in the game while being chased in a cave by a large creature (trying not to spoil anything). It doesn't matter how many times I play it because it works on the idea that your life is genuinely in jeopardy, but you have no idea how close to death you actually are. This never happens in F.E.A.R. I couldn't feel afraid because it just wasn't threatening, every time Alma popped up I thought, so what? What's next, you'll wave your arms around and go "whhhhhhoooOooOo, I'm gonna getcha, I'm gonna getcha!".