Want a challenge? Good.
First let me say that the game becomes quite challenging after you finish your first run through the beginning levels / tracks. For the most part, this is a VERY good thing. On several occasions, I felt my shoulders physically tense as I was nearing the finish line knowing that the next car was .01 seconds behind me. Did I break too much in that final turn? Did I miss my turn line and squeal the tires for a fraction of a second too long? Would I win? Winning feels like an accomplishment once the training is done, and that's what I was hoping for.
Second, though, this difficulty is made a bit needlessly hard without the addition of a mini-map. On almost every track, there is a turn or two that, if you take it at all too fast, spins you out in the gravel. At that point, catching up to the other cars can be great fun -- until you spin out again. The problem here is that you can't so easily memorize each track (or I can't), and you end up on the verge of some great frustration unless/until you run a track so many times that you DO begin to memorize it. A mini-map would aid this issue greatly, even if it's less realistic. Yes, you can have the game auto-brake for you, but this pretty much means either too much brake when you don't need it or still not enough when you do. I think ultimately you want some assistance, but the app itself doesn't seem to evaluate these steep turns as well as it does regular turns.
Finally, all the production values are very good. The music great. The load screens are great. The cars are great, and so are the tracks themselves. You have a number of input options that range from the game auto-breaking completely for you or just a bit - it's up to you. You have two views, a cockpit and a 3rd person view behind and above the car. On my first generation iPhone, the game runs very well with only the very occasional stutter (which, sadly, means I usually wreck, but it's rare).
Basically I was in the market to buy ONE racing game for my iPhone and not regret the purchase. Real Racing has more than exceeded that goal. I am taking a break simply because of some of the difficulty frustrations, but I very much like that I have a TON of racing still left to go if I want to win all the challenges ahead.