Red Faction 1 is fun. I played it again a few weeks ago. It's like a poor man's Half-Life with blowing shit up.
I agree with what slime was saying. The best part of Geomod in Red Faction 1 was the glass house tech demo level. In the actual game there were few times when it really was useful, though, when it did it was cool. One instance I blew a hole right behind a turret, then cleared the room out using that turret as a stealth attack.