I will explain. First and foremost, 99% of reviewers never understand the point of driving sims and give terribly myopic reviews. Second, it is important to make this distinction. Forza 3 is a FAR superior video game to GT5, in almost every way. Again, almost.
GT5 has 3 things going for it, ambition, the act of driving in the game with a wheel, and the authenticity of both the cars and tracks.
For example, look at the Top Gear review of the Audi R8 v10 and the Corvette ZR1. The Audi is a overall far superior car, but in the end the Corvette is the one that steals your heart. Thats how I feel about GT5. It has soooooo many stupid flaws, but when you get in a ZR1 take it to The Ring at 6am as the sun rises, tires still cold, HUD off, with your G25 in hand the quality of the experience is only rivaled by a select few. I forget my reality that I am sitting in my college dorm room and I realize the dream that I am actually at the Nurburgring. In FM3 I always know I am playing a video game. Most of this is due to (IMO) the cartoony/stylized graphics. The only blemish on this experience in GT5 are the sounds, and the blocky shadows.
GT5 tried to do soooo many things. Weather, day night cycles, rally racing, Nascar, endurance racing, and on and on. And while yes it did fail at some of those, it gets major points for trying when no one else would.
Lastly, I cannot forgive FM3 for absolutely butchering the rendering of certain tracks, particularly The Ring. Making a track that is known for its narrow corners, wider so that "more people can enjoy the game" is just fucking bullshit and really perturbs me. Add to that steering buffer and you have enough provocation for me to justify my opinion.
FM3 was the game that enjoyed but stopped playing, GT5 is the game that sometimes I cannot stand, but keep coming back to.
And for Shift, well, its a game/series that had potential but was invaded by focus groups and marketing. EA has to go around getting racing drivers to talk about "immersive experiences" and "what real racing is" to make this game sound good. Also if you look at the dev interviews, they always say "immersion" not "realism". Well I have got news for you, realism is IMMERSION! Immersion is not a guise for realism. Michael Bay movies are not more "realistic" because they have dramatic camera angles and cool special effects.
While yes, racing drivers do move their heads, its their eyes that are the key element, constantly scanning, focusing on points of interest, looking for not only the apex, but for marbles that may have accumulated on the side of the road, the nuances of the car in front, probing for a weakness, etc, etc.
There are so many things that a driver focuses on that trying to replicate the experience with a simple head movement and motion blur is really quite silly.
I will leave you with this:
http://dai.ly/h4nuZd
http://dai.ly/dPUEhQ
Still some of the best GT5 videos around.