You speed through a set of tunnels on a mission to destroy your enemy's ultimate weapon. The tunnels are filled with enemy vehicles, choppers and sentry guns which you have to wither take out or avoid. To make life even worse, a lot of sections require you to clear them within a given time limit. The only good thing is that you'll be able to upgrade your weaponry often.
So basically you'll spend most of your time racing through a complex set of tunnels... really, really fast.