From what I know of FC3, the variety of opponents mostly came from animals and heavily armored humans, right?!? Personally I don't really like the approach, since we are talking about animals as they actually exist. Yet the world was still filled to the brim with them. And in addition they were a ressource. While I understand, that Ubisoft tried to make exploration/interaction with the environment more important, it doesn't exactly feel very believable, does it?!? We are not talking about a fantasy/sci-fi-setting here. And even that would often not be an excuse, since even such settings should adhere to some rules.
Also, was the behaviour of the animals actually varied? I'm asking, because it certainly was the case in the STALKER-games. Also, the fact, that the exclusion-zone is basically a wilderness helped make the masses of mutants everywhere a little bit more believable. Same for the mutant-body parts. It makes more sense, that scientists would be interested in the mutations, rather than just murdering off the environment because somebody told you to, or because you want to make random stuff from it. Talk about gamey.
I guess it is in vain to hope that they would try to go back to some of the strengths of Far Cry 2. I'm not saying it was flawless, but apparently the level of gamey bullshit was far, far lower.