I picked this game up for fairly cheap on one of those Steam summer sales, and it's actually pretty good. It's fairly open world in that there are open zones... as you conquer a zone for the red faction (the martian liberation basically) you open up new zones. Travel from zone-to-zone is open-world... no load screens or anything. Mostly the world is just red hills and red plains... gets a bit repetitive, but it's freakin' Mars, so I guess that makes sense.
There are a bunch of vehicles you can commandeer, but the best thing is blowing up shit. Basically any vehicle or structure can be destroyed. You were a demolitions mining expert, so you carry along demo charges you can plant and then detonate. You can buy upgrades and new weapons and whatnot with 'scrap' you collect after blowing shit up. You also have a sledge hammer you can use.. given enough time, you can take down any building or vehicle using just your sledge hammer.
The building construction is pretty flimsy, but it sort of fits. It also seems like the building are very lightweight (fits again). It's possible to bash out 3/4 of a building's ground floor and it'll still stand. The best is setting a whole series of explosives around the ground floor of a building, backing up, then detonating it and watching the explosions ripple and crap blowing up everywhere. On more than one occasion, I think that it was sufficient, then the whole structure will come tumbling down.
Anyway, I'm only in a few hours, so it's possible I'll get bored with the mechanic, but so far it's keeping me quite happy. In some ways it's similar to Just Cause 2, but in JC2 you can only blow up some things.. in red faction you can blow up freakin' anything.
It sounds pretty fucking cool! Can you kill tanks with your hammer too? 
And there's tons of stuff I missed... like there are secret audio recordings that you can uncover to unlock super bombs or something. I found 3 and unlocked MOAB, but wasn't really able to use it like I would have liked. 
