A gorgeous environment, diverse cast, and interesting gameplay mechanics make up for the minor flaws.
I believe that Far Cry 2 is very underrated, it has many interesting concepts that make it an overall fun game. FC2 is slow at first, but the pace quickly picks up once you get the hang of the environment. A common complaint about this game is the mercenary fights that break out every few minutes. These can be avoided by using stealth, crawling behind bushes and going around intersections will get you where you need to be with very little conflict. It also encourages you to take over guard posts.
What is very interesting about FC2 is the everlasting effects of your actions. If you burn down a tree or field, it doesn't grow back. It stays burned forever. If you blow up a car, the charred remains will always remain. The game runs in 24-hour cycles. You play through dawn, day, dusk, and night. Throughout every hour of the day, the environments look amazing. The shadows are impressive, as they move as the earth rotates. The bushes move, and can be chopped apart, the clouds in the sky move, the grass and trees blow in the wind.
What also impresses me is the realism in this game. You must physically hold a map if you want to use it, and it doesn't pause while looking at the map. If your car breaks down, you must briefly repair it by tightening a few bolts on the engine, if you receive a serious injury you must dig the bullet out of your body, snap a bone back in place, disinfect a wound, or pat yourself out if you catch fire. You also have malaria throughout the entire game, and must take a pill every 30 minutes (real time) to combat the effects. If you run out of these pills, you must complete missions to get more. Your guns will also start to jam after being overly-used or submersed in water. These can all be annoying at times, but it makes the game seem so much more realistic.
Overall, Far Cry 2 is a good game to play if you like games where you have the freedom to do whatever you like, whenever you like, however you like. There really are no boundaries to what you can do in this game. It's like Grand Theft Auto in the setting of Africa. The gameplay is said to take over 50 hours, I'm only nine hours into the game and I'm loving it more every minute. :)