Isn't his granddaughter Susan living on earth in 2150? After the Dalek invasion of that year was defeated she fell in love with a guy called David Campbell and stayed with him. So could the Doctor not go and visit her? After all when he left her there he did say "And one day I'll come back".
I was disappointed, five out of ten at best. I really do hate those episodes where they throw in absolutely everything (what happened to the Angels in the snow?) and the Doctor becomes a sort of god-like figure: quasi-immortal and the saviour of the entire universe.