The handling is great, the graphics I expect to be fantastic. They just need to sort out some of the inconsistencies. I expect to see weather and day/night cycle for every track. Both of these were more hardware limitations on PS3 so I expect to see those sorted out. The sound needs drastic improvement. I want to hear gear changes, I want to hear the bodywork rattling at high speed in the cockpit view and so on.
After that they really desperately need to change the actual game's structure. Playing a GT game as a game is a boring, turgid experience, and has been for several games. They've literally not innovated or changed it up much at all since the first game. For a game acting as a real racing simulator, so much of the game feels completely at odds with anything that resembles real racing. Weird cups featuring Toyota Yaris' and Honda Jazz's or whatever. It's dire, boring and the game feels like a grind from the very first event. A grind that really is not all that enjoyable as the racing itself hasn't improved much. AI cars hold to the racing line, they always break, usually way too early, at the same point even though most decent players break at a later point and often take different lines. It needs improved, it needs to reflect how real racing drivers would drive, it needs to have some variability, some believable AI mistakes and heroic moments.
For me I buy GT to get the chance to drive the cars I want around the tracks I want (and was my best option not having a gaming PC), but the game locks away everything from the start and the grind is the only way to unlock better cars. Game after game. Project Cars nails what a racing game should be about, actually letting you race, letting you drive the cars you want to the minute you start the game. GT should just give up the ghost on forcing you to grind and "play the game" to get you to that point and follow Project Car's lead.
If you provide high quality racing experience and good championships that reflect the real life ones then people will happily drive slower cars, when it's fun and there's a real challenge there. I don't think everyone, or even most people who buy GT buy it to grind and play the game to unlock ever faster cars. Even with fast cars unlocked I still get a lot of joy rifling around the Nordshcleife in an Evo X. So I don't think it will ruin the game for most people.