Red Faction: Guerilla gives players few options: drive around, shoot guys, destroy stuff. Though this sounds limiting, it executes its core concepts well and gives player tools to do the job, and generally leaves the details up to us.
The game has you destroying bases and completing missions around the surface of Mars in order to increase your faction influence over an area. Blow up buildings, save hostages, drop a progress bar or two, and suddenly you've unlocked the next plot point. You can choose to play these progression missions, or continue to wreak havoc on the poor, unfortunante, totalitarian, well armed, persistent Earth Defense Force at your leisure.
Thankfully, you're not always alone.
Unfortunately, these AI controlled helpers can sometimes do more harm than good. Certain missions assign you a few these NPC's who ride along with you and help you through combat. When these helpers don't work is when they appear as generic "reinforcements" in the game world, apart from specific objectives. These allies "help", but also crowd the player incessantly, often ending up under your bumper, and never mount up alongside you.
The missions themselves give you plenty of choice in your courses of action, failure can cause some frustration. Usually starting some distance away, you spend plenty of time driving, repeatedly if you have to re-try. If you forget to reinitialize the mission after failing, you can waste time going towards objectives you've forgotten to re-start. Additionally, the unobtrusive health bar sometimes leaves you more drained than you realize after firefights, and it's not hard to die suddenly from a stray bridge collapsing on your head. The lack of consistent mid-mission checkpoints is another annoyance, you're not always sure how far back you'll be set, and I don't recall checkpoints at all outside of the major "story" missions, though those are also inconsistent in their spacing.
Complaints aside, the core of the gameplay is well implemented, despite it's overall lack of variation in objectives. Though a "shooter", driving makes up a large chunk of content, though getting past the Martian, slightly floaty learning curve isn't much trouble. Weapons are variants on "exploding" and "shooting", topped off with a good heap of sledge to the face. There's enough weapon variety to let you suit combat to your preferences (I enjoyed a mid range nano-rifle + rocket launcher combo). A highlight is the demolition physics engine, hammering away beams to bring a warehouse collapsing down on top of enemies exemplifies how the improvisational game play shines.
The story is fairly straightforward, just enough to point you at the next installation to raze, and the environments are all variants on "rocky, industrial" landscapes, but the open world and solid mayhem gel nicely, despite the occasional frustration. Red Faction Guerilla is a good example of a game whose novel and well implemented design principles elevate it away from being just another unremarkable action title, ending up with a fairly memorable, personalized, and explosive, gameplay experience.