There's a new 1st PERSON SHOOTER in town, and the boys at Bungie should turn and take notice. FAR CRY is exceptional
Another noticeable upgrade is the enemy AI. No longer do enemies just stand around ready to be shot at. If they know you're around....they will Charge You, Find Cover, and even send out guys to Flank You.
If I had to find a complaint, it would be in the driving of Vehicles, which can be somewhat clumsy at times, though eventually you start to get the hang of it.
It's just a month away from HALF LIFE 2, and this game will easily fill that time.