YouTube - Red Faction Guerrilla: Destruction (Game Trailer)
I downloaded the demo yesterday, very fun. What I like is that the destruction is there, but the game isn't all about "OMG blow up the buildings!" The gameplay actually gives you the choice. I played it a few times, the first time plowing through buildings in a giant armored car, the second time I used stealth and made and got to the objective without being seen and only killed about 2 people. The AI is also very fun to play against.
When you start out, the enemy AI wont start attacking you unless you get too close to one of their bases or if you start shooting at them. The neutral AI can either help you or remain neutral. If you go out and steal on of their vehicles, or kill one of them, they will identify you as a thread and stay away from you. But I've found if you help them out by destroying the enemy faction that is controlling their city, they begin to help. The game does the open world thing so well, with so little frusteration and flaws that I often see in other open world games.