The unusual problems with the g++-5 transition are:
Another big one is the descision was taken NOT to change the sonames when making sub-transitions. I presume this was done to avoid deviating from upstream sonmaes but the flip side has been that major sub-transitions have become "all or nothing". Afaict this is the biggest contributor to the upgrade pain that testing and unstable users are experiancing and it will also likely be a major source of pain down the line for people trying to migrate from jessie to stretch.