Far Cry 2 is perhaps best known for its strange array of "realistic" features, such as malaria. You may be glad to hear that Ubisoft is tossing that idea, and others, out the window for Far Cry 3.
Producer Dan Hay told Kotaku that guns no longer rust and your character no longer has to take malaria medicine. Furthermore, you no longer need to spend ten minutes driving to a mission. The devs have implemented a fast travel system that's hopefully more robust than the buses from FC2. The changes were made due to fan feedback.
In FC2's campaign, players were accompanied on missions by non-player characters that could die permanently. That feature has also been cut for the third installment. While it was a noble attempt to make gunfights more meaningful, those companions were kind of a pain in the ass. I ended up just reloading the game whenever they died. Also, if memory serves, they were a bit flakey when I needed help.
There is one way that FC3 is more realistic than its predecessor, though. If you wipe out a base of enemies, they stay dead. They don't reappear as though nothing happened.
"Realism" always seems like an admirable quality for a game but once it makes the experience less fun, well, screw it. Swapping my AK47 for another AK47 after every gunfight was a pain in the ass, and so was driving to every mission. The time spent foraging for a new weapon or commuting to a new objective was, essentially, empty time. Ubisoft seems to understand this now.
Far Cry 3 will launch this fall on the PS3, Xbox 360 and PC.