1. Since GT Sport has a livery editor, we need it to be like that of Forza (in terms of functionality, like in Motorsport 6 and Horizon 3) but with an added bonus where you can not only paint cars you don't own, but also use liveries on them (like for cars in Arcade mode that you don't own). In Forza you need to buy cars to save downloaded liveries, but with GT Sport you can save any livery you want for a particular car, regardless if you own it in your Garage or not.
2. Practice/qualifying in career, arcade and online and the return of A-Spec/B-Spec (GT4-style with GT5's own concept similar to Motorsport Manager) for both career, arcade and online.
3. A traditional career mode like in the original Project CARS to differentiate from the game's vague "Campaign" mode, so at least we can play something, and even earn Credits to buy and customize cars.
4. Custom championships for Arcade, the ability to hand-select cars for the AI (like in Motorsport 4, even with custom liveries) and as well as the return of Machine Tests for all cars as a mode in Arcade mode
5. A damage engine as good as that of Motorsport 4 with Assetto Corsa's mechanical damage simulation, plus rollover physics
6. Since they teased what could be Forzavista in GT Sport (only through PS VR), this Forzavista mode should also be accessible without a PS VR.
I could list many more, but these are the six features I really want to see.
The sounds are actually very nice, but some work needs to be done with the shifting sounds (and the simulation of shifting), and we can't just hear the same turbo blow-off valve/waste gate sounds for most of the cars. The graphics also look very clear as well, and that's no problem.