This game was awesome. The environment is just incredible - that would have to be my favorite part of the whole game. It's extremely well done.
However, you can't help but feel like there's a lot of untapped potential, and some fairly serious design flaws. For instance, having every guard post and roving vehicle shoot at you on sight was an absolutely terrible decision. It makes you wary of exploring, since you'll likely have to get out of your vehicle and deal with some enemies every 30-60 seconds. It takes fucking forever to get anywhere; if they didn't have the bus stations, I would have quit the game. You should be able to ally yourself with a faction and drive safely through their guard outposts, at the very least (the game has to make up an excuse for why this is not so). And remove the roving vehicles entirely. Also, the stealth aspect of the game felt underdeveloped - it was possible, but frustrating. The course of events usually involved picking off maybe one or two enemies without being noticed before the shit hits the fan and you have to go loud.
As for untapped potential, I would have liked to see a lot more RPG elements added to the mix. Some are already there; unlocking weapons, exploring to find diamonds, some side missions. However, being able to walk into a guard outpost/town (WITHOUT being shot at) and talk to a character to receive a side mission would have vastly increased the depth of the game. Honestly, there were times when I was driving around that I got a Morrowind-esque feel from the game - but only that. It was so close to being utterly amazing.
One point that really interested me is that the story is thematically based on Heart of Darkness - or was supposed to be, anyway. Some parts of that idea are still present, albeit in an altered form. Malaria is one such part. In an interview early on in development, one of the devs said that you would be able to do underground missions for malaria medicine at the start, but as your reputation for violence rose they would stop being offered, and you would slowly degenerate into madness. The last part was taken out however, and now all that's left is an annoying game mechanic requiring you to take missions for malaria medicine from time to time. Anyone who has played the game and read the book will be able to spot other parallels (including the final area very subtly being named the heart of darkness).
So most of the game was pretty cool. The weapons were fun to use, although fire turned out to be just a gimmick. It's far easier to just shoot enemies than start a brushfire that spreads into their base. The mortar wins my vote as coolest video game weapon this year, by far. All is good, and then we get to the finale.
The finale. Oh dear.
I'd better spoiler this next part, since it regards the finale/ending.
The ending itself was decent I suppose, although the one with you detonating explosives could have had more of an effect than the screen turning black suddenly. Heck, even making it turn white would have been an improvement. The other ending involving you shooting yourself felt unfinished, because you just go talk to the guard and the game ends. I was hoping for an emotionally powerful scene reminiscent of the one from Call of Duty 4 in the aftermath of the nuclear explosion, but was left disappointed. We see a brief cutscene of the journalist, then are told the aftermath with text.
All in all, I would definitely recommend picking this game up. It's an experience, that's for sure.