It's one of those movies, that you can't hate, but you can't like, too.
There is nothing particularly wrong with the movie. It looks good, the story overall is ok, too. But it feels kind of... Empty? Pointless? I did not feel much of a challenge in Jann reaching his dream, even though, I'm pretty sure, it was not that easy. Since there is no challenge, and since we already know how things will end (thanks to marketing) - there is absolutely no tension, there are no real stakes, there is no... Excitement. Which is core of racing, is it not?
I remember people complaining that anime "Overtake!" lacked excitement in its racing, which was a valid criticism, but, at the least, it had something besides that: character development. It was not perfect, but it was there. Gran Turismo lacks even that. Or at least, I have not noticed any development. Besides, maybe, Jack Salter starting to believe that gamer can become a racer, after all.
The original story is something that can inspire. That's what all the marketing was talking about: "achieve your dream". But achieving a dream is not easy. There are struggles involved there. Yes, they probably will not be as intense as being in literal war, but they will be there. A movie - is a great opportunity to dramatize those struggles, to make you feel the tension of going against the flow.
This movie fails at that. Unless you think integrating elements from a game user interface equates to dramatization. I will forget this movie by tomorrow.