Well, I got my copy today. Quick review: oh dear !!!
Opens with a classic track (O Fortuna) that i really like but it could get really tiresome after a while.
I went to the options menu and turned all assists off except ABS. Simulation mode, 'legend' skill (don't laugh!!

), and went for a few laps. Started off in the DBR9 at the Nurburgring (GP track folks, no Nordschleife here) and the handling is quite diabolical ! Feels quite arcady, and has a little of the pendulum effect as you correct, overcorrect, correct again.
I thought the race lines were more like the lines you'd take on a motorbike, early entry to the corners, and it took a while to get to grips with that.
Very understeery too....
Had very little joy in the Aston Martin, so tried the Pagani Zonda, even worse with no grip, by comparison. So, onto the Enzo. Ah, this is a little more like it. Decent grip, mostly predictable handling. Did a few tours at Spa.... its been YEARS since I've driven a (virtual) car round there, and then onto Mugello, another proper European 'open' circuit.
Overall I fared rather badly. So went into the tutorial mode hopefully to get a few hints from Tiff. But he was no help at all, besides i couldn't hear what he was saying above the engine noise. Then i thought, OK, I'll turn on subtitles so i can SEE what he is saying. But that was even worse as the subtitles are delayed a few seconds, so when you read BRAKE, BRAKE, BRAKE... you've almost got yourself out of the sandpit anyway.
So after 126 Miles I took a break, and overall I'm underwhelmed. This is NO Gran Turismo 5, hell its not even GT5 prologue.
But if I have anything good to say about it, its the sound. We've discussed long and hard how Polyphony just does not impress with GT sounds, and Supercar Challenge is a fair example of the way GT5 should be heading with audio. Gutteral, evocative, spitting, snarling, mean ass engine sounds is what SC has. Its not perfect, but it really does involve a lot more aurally than any GT game I've played.
The track selection is reasonable, but on the few I drove on, they don't appear to be 'measured' too well.
SC is in my estimation, unfinished, unpolished, and unsurprisingly cannot touch Gran Turismo 5 Prologue in virtually any area (Except of course the amount of content, specifically tracks). Pehaps its a little unfair to compare it directly to the 100t elephant that is Gran Turismo, but they are after all direct competitors vying for the same market.
No surprises there then....