I'm with Brid-Aine on this
Her review sums up almost all my frustrations with this anti-climatic end to the series. But I'd like to add another.
Unless the whole of humanity have been burying their dead in metal coffins, how did the corpses all reanimate with full cyberman armour? I'll give the writers the benefit of the doubt over the whole cyber-pollen thing, even though it's a blatant rip off of borg nanites, but I'm not having this conjuring up armour from thin air.