However, the biggest one was the online lobby system.
Quickly joined a game room, entered the track, and seamlessly starting doing time trials as other players raced around, pitted, entered in and out of the game room, etc. The speed and smoothest you can join public 'rooms' where you can just do laps, clean racing, etc -- that's probably sold me on the game.
The ability to just seamlessly join open 'tracks' with people, and not having to sit in a lobby and wait together for a race to start, is pretty huge. It's not a unique feature, and other genres (e.g. Ground Control 2 for RTS games) have done it many times before...
But GTS seems to do it really well and especially with the track, time trial, 'perfecting your track time,' etc spirit to the game I think it's going to result in a pretty awesome car appreciating and race celebrating community ... A sort of 'track' culture, distinct from 'racing' culture in in that it's less combative. Between online gameplay and interface production, the game has a lot of ways it could do to promote a positive community.
I think, when all is said and done about bells and whistles, review scores, graphics face-offs, etc, what really could shine about GTS is its online component and a sort of 'track' culture.
This is precisely what I was hoping for, and what I think a lot of people in the lead up have missed about what this game is trying to be. Gran Turismo Sport is designed to deliver on a convenient online experience focused on balanced and fair racing, and while some may consider that to be an easy feat, it isn't something that has been done before.