Just Cause 2. Pretty much all I've been playing since Christmas.
Imagine GTA IV mixed with a bit of Far-Cry 1 and make everything waaay over the top. Like on only the 2nd or 3rd mission I did I was sabotaging space rockets on the launch pad and stealing aircraft to shoot down one that already took off, that kind of over the top.
You have a grappling hook which you can reel yourself into stuff with, an example of gameplay might be you running from the cops and stealing one of theor motorbikes. As as you ride away you pass a car which you decide is better than the bike, so you grapple onto it from 30m away and pull yourself in and stand on the roof, then either car-surf, shooting at the cops (you can also climb around on the car to get a better position) or hijack it and drive yourself. You also have a parachute, so you can grapple something, reel yourself in and open the chute, so paraglide up into the air.
A cool thing is you can use your grappling hook to join two objects together, so you might attach your car to a statue and pull it over. A particularly cool thing I did the other day was running out of ammo and being badly injured while attacking a military base. I came round the corner of a building to find a guy with a mounted machine gun, so shot him with my grapple and pulled him out from behind his gun. As I did this, I saw a fighter plane taking off on the runway behind him, so fired my grapple into him again, and then into the plane, causing the plane to take off towing the guy along behind it.
There's a demo on Steam (and other places I imagine), you should check it out.
it runs fine at medium though
