I've been running RR3 for a few months, and it's quite addictive. I don't recommend this to anyone who has no free time, because it takes a while to learn it, and then you have to get new cars and learn more.
There are a few things to keep in mind if you want to play it for free.
1) Don't spend any Gold on Upgrades. You don't need the God Upgrades to win any of the races. But you do need to learn how to drive without the assists. The way they hook you into buying Gold is allowing you to spend the Gold you earn on silly things, like upgrades that you don't need. Then, when you get to where you need the Gold to buy cars that require Gold, you don't have it [or it will take you a month to earn it now that you have won all the easy matches].
Instead of spending Gold on Upgrades [yes, spend money on them until you can win, then drive the hell out of it], learn to drive without the Assists. It's hard as hell at first, but you get used to it very quickly.
2) Crash through the AIs on short [1-2 lap] races, because you have to if you want to win. But avoid them on races 3 laps or more, because you kill your car and they run you down at the end.
3) Have Patience. It's not the car's fault. They are all different, and that is what makes it fun [I wish they were all like that Lamborghini I just drove].
They have a new version out that lets you see where you rank with everyone else in the world, and also with some group that you are in [not sure how they group you, but it looks like it's based on your equipment, and maybe your time behind the wheel]. That's a wonderful thing, but it will bring you right down when you find out that your rank like 320,000th on the race you just ran, when you thought you were flying, lol.
It's the most awesome game on the planet [for an iPhone], and it's free, so it's bound to get big.