Yes, its a pay to play game, yes it can cost you a whack of money if you have no patience, but overall the game is built so that you have to race over and over to get cash to perform upgrades. Imported upgrades cost gold to deliver immediately or it has a timer. Gas costs gold or wait for timer to refill tank. A new car costs gold to deliver immediately or has a timer.
Where the stopping point is at Tier 4, cant buy a Tier 4/5 car without using Gold and gold is an in app purchase. Yes, you can win a T4/T5 car by beating the crew leader in crew battles (I assume because I am at Tier 3). One reviewer noted that you had to buy the special NOS to win a crew battle, this is not the case if you have the right car and all its upgrades… Daily championships are 3 races long and easy money as the two cars are identical so it comes down to shifting skill and NOS timing to win all 3 and get a gold coin...
It falls down in not telling you in the game which car is FWD, RWD or AWD (Some specialty races require certain types of cars) and I have asked for this to be included in the specs of the car with HP, Weight, Grip, Transmission.
Game Center suport seems to be lacking a bit, I am missing some badges that I should have earned but there is also a tech request in for that.
Overall I give it a 5 star rating because it has potential and with some bug fixes, difficulty balancing and not so many IAPs it would be outstanding for a long time play game day after day. I very much enjoy it!
I have built a Numbers spreadsheet with certain car details, I will be sending it to the developers to add to their website if they desire.