GT2 is ancient but the fact that I can play it on my Retroid Pocket anywhere and enjoy a stupid variety of cars, customization, tuning and racing fun has me always going back to it.
Of all the Forza games, FM4 is pretty great and I haven't liked any of the newer ones. I need to get my 360 back from my friend I loaned it to during Covid specifically to just play that one game. That was peak for that series I think but I haven't played FM2.
Test Drive Le Mans is excellent as well for circuit racing.