Far Cry 2 suffered from some incredibly stoopid game mechanics. Crossroads at central points in the game respawn within minutes of you wiping out the crew manning it. You drive somewhere, turn right around, and the crossroad will be full of guys again. They even knew this was a problem in testing, but made the decision that it was somehow too 'troublesome' to change before release.
Also, the so called story is totally devoid of anything resembling characterization, motivation, or....story. They let you choose from a bunch of different character background types - none of which are different in anything other than looks. You hate the bad guy, because....well they say you hate him. He supplies weapons to mercs! Most of the game, you, a merc, are trying to expand your supply of weapons. I guess they slept through storytelling 101.
Good engine, looks nice, but only fun as a mindless shooter. Not worth the $5 I paid for it, personally.