This is a matter of one of those perception things, because "sterile" to me are PC sims. Very clinical, technical, rote, structured, bots as boring as the previous Gran Turismos, and cruddy graphics until this new generation of Project CARS and Asetto Corsa. Plus, very limited car lists, usually with liveries that I don't care for. Every car feels like a loaner.
Gran Turismo has somehow made car racing and collecting fun. Cool. I don't know what it is, but each game is something of an experience I can hardly wait for. And GT6 has taken the series to a new level in almost every way, even unfinished! There are a LOT of additions the team are working on for us, not the least of which is Course Maker II. Racing against bots is a blast now, though I intentionally keep my car 50 to 100PP below the race limit, except for extreme cases or if I just want to blast through it. It's pretty clear that PD has pushed the PS3 about as far as it can go, so I'm anxious to see what they can do on PS4. But this game is ridiculously cool, and when the camera pans across the vastness of Willow Springs, it takes my breath away. And it doesn't hurt that a number of the Standards are close to Premium level now.
Other racing games have their own benefits, and PC sims have slightly better physics. But Kaz gave us a series that brought racing sims out of the niche market and turned millions of us around the world into car nuts, and GT fans. And when Microsoft wanted to make a flagship racing series, who did they copy?