The story isn't really that great, but there's enough there to make you see it through to the end. While the story missions seem varied in the start, they don't really get much better as you progress; instead they only feel more tedious. But there are some cool missions in there.
One that particularly stood out for me was a stealth-driving mission, where you're required to drive through narrow alleys and stay under the police radar. And to make things more interesting, there's a ticking time bomb in the car, and the car doesn't have brakes; just the handbrake. There are a few other interesting missions as well, but they're few and far between.
You also have a bunch of optional side-missions. These include checkpoint races, time trials, taxi missions, and rampage, similar to Cost to the State in recent Need for Speed games. Depending on how well you perform in these side missions, you are awarded a grade. Achieving an A or S (highest) grade earns you bonuses such as ammo pick up points or additional armour for your vehicle, allowing it to withstand more punishment.
While these incentives should add a reasonable amount of depth to the game, the side missions themselves aren't really that appealing. Besides, the game never really gets difficult enough for you to require a perk like added vehicle armour, especially with the airjack option available to you. You also earn money in side missions, but there's no place for you to spend it, so why bother?