Guerrilla's Geomod is used as a cloak to hide the fact that this is just a plain free-roaming game.
The game looks very good, the graphics may not be the best you'll see, but they're up to scratch. Planet Mars does look rather believable, if a little plain and dusty, and Alec Mason is a character you'll probably find yourself getting to like. There is also a lot to do in the world of Guerrilla with many side-missions to complete and other secrets and weapons to unlock. Plus, if you ever get bored of the single player, there's always a fun online mode to play or a 'pass the controller' type of mode that sort of makes up for the fact that Guerrilla lacks split-screen.
You could say that Guerrilla has taken a few pages out of Mercenaries's book and done a better job of the destruction. Basically, if you're looking for some fun both offline and online, you'll probably want to grab yourself a copy of this game, but if you're looking for a little bit more story and interactivity, there are better places to look. Red Faction has done a good job and in some ways this game is much better than it's previous in the series, but there's still a bit more work that needs doing.