I honestly just love a perfect car racing game. I want hundreds of cars. Every make and model should be represented, with different years and trim levels available. I loved the detail of Forza 4 ,where you could tour inside certain cars and even get history of the cars. The focus of the game would customization and would allow if the real possibilities like motor swaps, drivetrain swap, and asperation conversions. But you also need to be able to turn that civic into a rice mobile. You need body kits, spoilers, and wheels for days to get that done.
The world would similar the best racing game ever (you guessed it) Need For Speed Underground 2. You get to drive around a city to go from race to race. There would events between and you could have some fun. The races would be at famous tracks like the nurumberg ring and you could expirence true racing. It would need different modes like grand turismo and Forza did. With an emphasis on drifting, which gets left out sometimes.
The physics would have to similar to Forza and focus on being a simulator. It would give you real time info on camber, toe, tire wear, engine heat, and telemetry all while driving. With a optional screen to allow you to tune your car for the perfect result. This would include engine tunes and boost changes. Everything would be named correctly, so might actually learn a thing or two.