...and you're questioning other peoples' intolerance of other views?
Next inane/abusive comment from you gets you a lengthy vacation. Practice what you preach, or don't post.
Not sure that had anything to do with SimonK's question, and you seem to have a hard time separating GT criticism from FM adoration (hint: they aren't always hand in hand). Drop the "fanboy" comments, too.
But, to answer your question: AI that isn't a funeral procession, like GT5. Better physics. A better car lineup (for my tastes, at any rate). Community involvement. More in-depth tuning. A better attempt at consistency across the entire game - GT5 has weather, and it is indeed fantastic, but it's only on a handful of tracks. That's not even touching the Standards/Premium issue.
Just some quick point forms, and this is hardly an exhaustive list. Then again, "best" racing game is an entirely personal opinion. For what I want out of a racing game, FM4 just happens to check off more of the boxes than GT5. GT5 has a few cars I miss that just aren't available in FM - yet - like the Cappuccino, a better, proper Nurburgring, a much better Photomode, and the afore-mentioned weather (and time) effects, but beyond that, it just doesn't hold my interest for as long these days.