First off, I want to state that giving FEAR an 8/10 does pain me somewhat. In so many ways, it's an incredibly awesome game, and some of the things that hurt my enjoyment might be considered features by other players, but I have to be fair, and rate it according to the fun I had playing it. This is the same metric I used with Doom3, and in some ways, it works similarly here.
FEAR is genuinely scary. Not scary like Doom3, where it's incessantly pitch black, and then there's eight hundred hidden doors that unload a monster behind you when you walk past. FEAR creates a mood early on, with a few spooky images or noises, a flitting shape in the corner of your eye, and for the rest of the game, you're constantly intimidated and scared. It's like the scene in the horror movie where somebody is slowly walking into the scary house, only in a movie you can cover your eyes, or look away, and things progress along. In this game, you're controlling the character, so nobody is gonna walk down the dark scary hallway but you. Over time, I got more accustomed to this element of the game, and it was also less emphasized in the map design, but early on, it was a bit much to take, to the point that it really did detract from my enjoyment. As I said, many players will consider this a feature, and I do have to compliment Monolith on making a genuinely scary game. Not startling, which is easy. Scary.
What really stands out in FEAR is the enemies. Their animations are incredibly diverse and lifelike. Their control over the environment, knocking over stuff to hide behind, vaulting over railings, is impressive. Their AI is solid, and they use grenades, backdoor and maneuver in ways that can be very difficult to deal with. When killed, they go so smoothly from their current activity into ragdoll physics, it's an impressive effect. They get knocked down and get back up. They limp. They stick their gun around corners and fire blindly. They even have a limited degree of destructive modelling to them. It's not quite the gory detail that the Soldier of Fortune games featured, but a close up shotgun blast will knock a head or limb off, and a direct grenade hit will vaporize an enemy entirely.
The quality enemies add to the combat experience. At first, I had a little trouble with the weapons - they didn't feel entirely right to me - but something clicked pretty quickly, and I learned to really enjoy them. They're noisy and do a lot of damage. They create realistic pockmarks in walls, kick up article effects or dust where they strike, send splatters of blood off enemies. There's a nice variety of weapons, although none are vastly better than the others, and only three can be carried at any one time. This creates a nice tactical puzzle, as one tries to trade off between firepower, effective range, availability of ammo, etc. across three weapon slots. I found myself most reliant on the Shotgun, as most of the game is indoors and at close range. The Shotgun combines nicely with the Slo-Mo effect, which is a special power afforded to your character. With the press of a button, time slows down for you, allowing you to carefully aim shots while the AI enemies contend with real time speed. You can sustain this power only for short bursts at a time, but it's usually enough to clear out a room with some carefully shotgunning.
Slo-Mo produced a particularly memorable effect for me, as I hit an enemy dead center with a shotgun blast, causing him to split in half at the waist... His legs collapsed realistically to the floor, while his torso flipped end over end in the air before falling atop them. All in glorious slow motion. Cool.
The graphic and physics engines are both great. Lighting effects in particular are very advanced, allowing for spooky tricks of all sorts, and generally adding to the realism. My X800XL seemed very capable of running the game with very high settings, but there were some performance issues at times, which peaked at one point later in the game, and then returned to a much more playable level. At times, particularly when looking around, the game will hitch, or lock up briefly, before returning to normal. This doesn't seem to be directly related to the rendering engine, as it can run very smoothly for extended periods. Instead, I'd speculate that it results from textures loading to memory, or some other IO task. For most of the game, it's just a minor irritation that generally occurs near the start of maps, but for one segment, the game did play quite choppily for me.
The story aspects of the game were interesting, and held things together, but a few too many loose ends were left open for my liking.
All in all, FEAR is a great game, with great AI, models, graphics, lighting and physics effects. It loses points for being a bit too scary at times, for the fairly repetitive level design, for the loose ends to the plot, and for some minor performance issues. My great hope is that Monolith will use their spectacular engine to make a new No One Lives Forever, as the previous two are some of my favorite FPSes of all time. Monolith is really one of the most underrated studios out there, capable of making as good an engine as anybody, and with a history of very entertaining titles.