I think people are forgetting the fact that Polyphony has more experience making games than Turn 10, this is Polyphony's 5th title, and only Turn 10's 3rd title. So, personally, I think Turn 10 has done a great job.
The fact of the matter is, these are both very well made and fun games. They are BOTH a racing fans dream game, Gran Turismo 5 is more hardcore, while Forza tries to mix hardcore and casual, and personally, I think they succeeded with it. Each game will have its flaws and good points, no game is perfect, deal with it. THey will both be good
I will have too say Team Fortress 2, that game is just full of epicness.