I won't claim to have spent hours on nKP, or tried every level of rain (hence I didn't know the first few clicks don't give you wets), or every car.
But I did play with the F3 car, the GP2 car and the Vintage in the wet (and the Hillclimb in the dry).
I like the wet. The puddles do seem to exist rather than the track being uniformly slippery. The front end wash out is also pretty realistic I think, exaggerated by being on a computer with no proper feel. It's SO easy in the wet to turn the wheels too much and start sliding towards the outside of the corner, and you have to crawl around at a snails pace - even though in reality the single seater in the pouring rain is going far faster than a good road car in the dry!!
The spray is a bit rubbish - not played multiplayer, but external cameras show the spray being rubbish. That's not a big concern though.
Overall I think it's a good effort at wet racing. It's a bit hard to spot the wetter areas and drier areas of the track, as the puddles don't seem to correspond to the glossy areas of track. But I do like having to feather the throttle and hold slight opposite lock on a straight in 4th gear because I've hit a puddle.
Has anyone done enough laps in the damp to see if a dry line appears?