Personally, I thought it to be a very good movie, with many fine details that really added up and had an impact. The movie had a well thought out and mostly correct timeline and chronology of events, but the time period is the thing that let the movie down.
The time period of the movie (set between 2008 and 2014) becomes confusing with many scenes with tiny details that could have been easily changed.
Some of these details include the cars. The first race that Jann enters after completing the Nissan GT academy features cars from 2020 (Aston Martin Vantage GT3), 2022 (Corvette C8 GT3), and 2016 (Ford GT GTE), all of which were made or released years after the movie was set. On the topic of cars, there was a scene featuring a Koenigsegg Gemera, which is a car that doesn't even go into mass-production until 2025, let-alone being in a movie set over a decade before.
Other features such as the opening scene with the development of the first Gran Turismo movie features scenes not from the original Gran Turismo, but the second most recent game (from the posting of this review) Gran Turismo Sport. The movie also features racing simulators and games from 2021 and 2022, not from 2014.
Other things like posters, and phone apps are also not to the date of the movie, but I suppose things like phone apps are harder to get older versions of if the phone activity was filmed, and not edited after.
I sound like a critique, picking the bad things out, but don't get me wrong, this is a good movie, just these minor details in my opinion, would make Gran Turismo such a better movie.