Ok, just finished it. Logged in about ~20 hours including replays, which were many cause I am incapable of hitting F5 periodically. Did it all on hard, which was a nice challenge. Graphics were very nice, even on medium-low (more medium). The sun rising on a river made me stop for a minute just to watch.
Spoilers
Ok, going to get right down to it. It looks as if this game was created with two teams: one incompetent and one at the top of their game. Every single level, every mission, every skirmish/battle up to the mountain was an absolute gem. I had a blast attacking every occupied base, using various methods ranging from sneaking in and silently killing to driving a jeep full speed into a large group before bailing out and blowing it up.
The amount of freedom was great and the physics added quite a bit to the game. The destructible buildings (sheds/small houses) were an amazing addition; I just went "wow" when I figured out that I could make my own doors by using strength and melee attack on walls. Shooting watch towers with rockets/frags actually brings them down, unlike almost every game before (sans Red Faction) where you need 5 shots to before putting one in the slit.
The nanosuit was cool and helped to add a lot of choice. However, I couldn't do much of what the trailer showed. It is easy to use and every ability was useful. I cycled through each of them at least once and actually used them for a while each level. Think it would have been a good idea to add some extra, customizable abilities though... too complicated for people probably... Weapons were pretty good, but the assault rifles were a bit similar and there could have been a few more. Otherwise, it was pretty well rounded. The customizability of add-ons was also incredibly useful. It was great to change out the scope and silencer when needed.
And the suck...
In short: everything alien. When the hell did the suit get thrusters for zero G? The alien weapon seemed weak. The aliens were retarded and could either strafe-rape you or just kill charge you. The way they made the aliens, there really isn't much I can think of in terms of how to improve them. They fly and have guns, look and act like squids/octopuses... They aren't interesting enemies and there is too little back story to them. Oh, and it became a rail shooter... an unwelcome change of pace.
Now the alien part isn't THAT bad, but it is crap compared to the first 3 quarters. I will be replaying it, but will call it a game when I get inside the mountain. They should have kept it to 2 arms and 2 legs or an even number of wheels...