Whilst I agree wholeheartedly with the comments already made about the retarded auto-respawning checkpoints, murderous AI who home in on your exact position if they catch sight of one pixel of you, etc there are some positives in the game.
Firstly, it looks great. As a showpiece for the DUNA engine it excels admirably. Whilst there will be some who debate about whether Crysis looks better, personally speaking I found Far Cry 2 to look just as good in "high" settings, at twice the FPS and at much higher resolutions. I can comfortably run the game in 2560x1600 on an almost bleeding-edge system and see things like this whereas in Crysis I could only run it in a much smaller resolution. In that respect, as an engine, it is a great technological accomplishment.
Secondly whilst the core AI had its faults there were aspects of it which made me ponder its deeper aspects. I came across one guy who was stuck inside a rock (not a great advert for AI granted) who I heard say "This is crazy I can't see anything from here". Another time, later in the game, I encountered two guys who whilst chattering made reference to a mercenary (me) who was "killing people from miles away". One of them remarked "you'll never see him coming, you'll just end up dead". Throughout the game I had been focusing on killing from afar with sniper rifles, very rarely bothering with CQC. Now, you could argue that this was just a coincidence but the accuracy of what they were saying was uncanny.
All in all whilst the core AI (checkpoints, zeroing in on fleeting targets, etc) seemed dumb, there were nuances to it which made me think there are layers under the surface and intrigued me enough to warrant completing the game.