My biggest issue is the lack of control over routing in general. I've several times been in the position where all routes on the navigation device pass through

My biggest issue is the lack of control over routing in general. I've several times been in the position where all routes on the navigation device pass through the road in front of me, yet I'm sitting in the car looking at a road closure. At that point I know there's a way round the obstruction, but the navigation is of no use in finding it. A simple "don't use this road" marker seems to me like a really useful feature, yet I've never seen it in any of the satellite navigation systems I've used.