I was already disappointed with GT5 that time of day and weather were reserved for a couple of tracks. More varied game play over fancier graphics any time. I would be happy with GT4 style graphics if that would mean it could run in 1080p60 with all tracks featuring dynamic time, cloud cover and weather.
I mostly played Sarthe and Nurburgring online in GT5, since the dynamic weather (with tire grip on real) made it a lot more interesting with pit strategy and tire choices. Shitting bricks when you're in the lead in the final lap by taking a gamble on riding out the rain while the pack is quickly catching up after changing their tires.
And tons of fun when its getting dark and you hear the people cursing that chose a concept car with no headlights :)
We need next gen for more real time weather change!







