How long exactly have you played it for? The action is however you choose to make it. You can run over hundreds of people, building up your wanted level having cops chasing you from everywhere. Then come the SWAT team, CIA, Helicopters, Army, soldiers, tanks! Throw a few grenades, watch cars go flying, rolling over, catching fire... Too much to list.
Also, as for the game not being multiplayer, BS! Bring it to a friends house and let the fun begin. See who can last the longest killing the most people and not being caught by cops. See who can do the best getaways. See who can do the most unique jumps. So many possibilities here...
Also did you try getting hookers yet? Stop a car by one and honk the horn. They will bend over and start talking to you. Soon they will get in. Drive them into a private place such as an alley and watch the sparks fly. Your car will start shaking and squeaking. It will start off slow, and keep increasing in speed. You will notice that your health gauge rises, up to 125%. Then after the hooker is done she will get out of the car and bend over breathing heavily. At this point you should get out of your car and beat her to death and get your money back.
God this game is great.
heh.