THE GOOD: I haven't been this impressed by enemy squad AI since going against Half-Life's marines. The clone soldiers appear to work in groups consisting of a leader, some subordinates, and sometimes a heavy weapons guy. Wiping out 2-3 of the group evokes a 'We can't stop him!!' from the survivors. Taking out their heavy weapons guy will reward you with a frantic 'He took out our heavy!'. The enemy will work to flush you out, keep you occupied, and flank you. Visually, on a top of the line system, FEAR is on par with anything out. Shooting boxes and files will send out a shower of floating confetti, a grenade will kick up a blinding cloud of dust, weapons fire will take out huge chunks of concrete from walls. Weapons and health kits are always on hand. Also, because of the incredibly adept enemy AI the developer, unlike others **coughID/DOOM3cough**, did not have to resort to ANY cheap kills. With the exception of a cloaking enemy unit, you will NEVER encounter some cheap enemy soldiers appearing out of nowhere behind your back. If you die it's because the enemy outsmarted you or you got reckless.
THE BAD: System requirements are pretty high. I've got a decent system(Athlon 64 - 3000+, 1GB RAM, 6800GT) and on medium-to-high settings it ran sluggishly on the larger levels. Enemy unit variation is somewhat lacking(about 6 total). Gameplay can get a little monotonous. The supernatural theme that the title has been hyped on is pretty much non-existant throughout most of the game, really only appearing in the beginning and ending acts.
OVERALL: Despite my gripes I still think FEAR is the best fps of 2005. The enemy AI is among the most lifelike I've played against - not perfect but you can almost see the enemy considering the situation and making the best decisions possible. The game looks good and the gameplay keeps you coming back for more.