From what i've been reading, a lot of people have been comparing the game as a whole to Rfactor with the real feel mod. But it seems the general consensus of opinion is, it's similar but better than RF. Can't really comment as i've never felt the need to get Rf, but i will say GTR Evo is definitely SimBins best effort to date.
The physics can't really compete with LFS or iRacing, but that's not to say they're bad. The cars never leave you with a WTF moment, but they're not quite as sublime and perhaps don't have those delicate little nuances that give you a warm glow in the pit of your stomach (know what i mean when i say that ?) Maybe i'm not the best at describing this sort of stuff. Perhaps things will improve when i sort out the wheel remoteness problem and get a few decent setups for the cars.
Bottom line is it's only £18 GBP and you get GTR Evo and Race 07 for that, so it's not gonna break the bank is it. And apparently there are a million and one tracks, cars and other mods to be found out there in interweb world, so it'll take a while to get bored with it.
Trick is, to go into it with an open mind and i think you'll be pleasantly surprised at how good it is. But if you expect it to be a competitor for iRacing or even LFS then i think you'll come away slightly disappointed.
I've only tried the Caterhams and the Radicals, not even so much as looked at the other cars tbh, but they are both very rewarding, fun cars to drive. Perhaps the lower powered Radical has a bit to much grip for my liking, but it's nothing a decent setup can't cure
And some of the tracks are fantastic. Istanbul is great, Brno looks plain but is really satisfying when you hook it up, and has a few hidden bumps that can easily catch you out, and Brands Hatch is a lot more challenging than i was expecting, and is all the better for it.
Go on buy it, you know you wanna, what you got to lose ?