It may be free but you'll stop playing it after you unlock all of the achievements.
In Doritos Dash of Destruction, you must choose to play as either a T-Rex or a Doritos delivery truck. As the T-Rex, your goal is to stomp around the city and eat all of the trucks delivering Doritos (because dinosaurs love Doritos). You will eventually compete against another T-Rex for who can eat the most trucks. As the delivery truck, your goal is to deliver Doritos to all of your destinations, while avoiding the T-Rex. Like the T-Rex, you will compete against another truck eventually.
That's pretty much it. There are only six levels but I beat both of them within like 10 or 15 minutes. You receive upgrades as you progress through the game as well, such as new and better parts for the truck and cybernetic parts for the T-Rex.
Also, this has got to be the easiest 200 gamer points I have ever gotten so if you're trying to collect achievements, this game will give you free 200 points.
There is only very little fun found here, but it's definitely A LOT better than Yaris. This game really isn't that great so you're not missing much if you decide to not download it but it is free, so you've got nothing to lose anyway. Although I haven't really touched it since I beat it.