Yes, I have to admit that the physics and AI have been concretelly improved vs GP3,we can't say the opposite.
Above all the AI is very impressive IMHO,anyway the game suffers heavy bug issues related not to the physics and AI but related to graphic instead.
Maybe GP4 seems easier to drive,but without any aids you can have a good challenging things to manage.
Tomorrow should be the judging day,talking about GC answers,and the next patch ( if it will be released ) will be the great judgement day.
Boomey