More sim than FM or GT, more fun than GT or FM, better looking than FM or GT. All in all taken what FM and GT did well and done it all better while leaving out what GT and FM did poorly or wasted too much time on.
If you want a game that does racing well the only game to get of this genre is Shift2. If you like collecting, painting, buying, selling, photographing and just driving cars then Forza and GT are the better car games.
I was mildly disappointed by FM3, I was massively disappointed by GT5, but I have been massively and pleasantly surprised by Shift 2