It's incredible. I have always loved the GT series, and this lives up to the hype. Worth every minute of the wait.
There will always be a handful of idiots that either "don't get it", and expect it to be a jump in arcade racer, or will think the wait has somehow devalued it's brilliance. Driving Monza or CoteDeAzure in a multitude of exotic (and non exotic) cars with realistic physics and modeling and draw dropping graphics is an amazing experience. GT has never been a 5 minute game, where you jump in a Ferarri and do all the tracks and then lose interest and move onto another game, it's about career building, starting in the lower ranks, driving normal racecars and then heading up the field with more more and better cars. Sure there is Arcade mode, but the real game is A-Spec.
It totally blows Forza3 out the water by a VERY long margin. Forza looks very dated by comparison, both graphically and physically.
Doing Nurburgring Nordschleife in the rain with fading daylight in a AMG Merc is an amazing experience.