It’s the sense of speed and degree of realism is higher than in Forza games. GT Sophy AI is also amazing. It adds personalities to the AI cars so they no longer follow predefined lines but they block, attack, crash or spin from too much throttle.
I’m addicted to Grand Turismo 7 right now. I don’t play anything else which is rare with me. I even got to the point where I bought PS VR2 just for this game.