Personally, I have found the ACC to be very poor. On A roads it often slows down to crawl for mild corners. On motorways it piles up behind the car in front and then hits the brakes at the set distance. Once the car in front moves away it hangs back then sticks the boot in to accelerate back up to speed. It's not the pleasant relaxing experience I hoped it would be at all.
On my previous car (VW) ACC smoothly slowed down behind slower cars and again smoothly accelerated back up to speed when the road was clear. It ignored corners on A roads completely mind!