Go me. Donna is a (partial) time lord. I called it. I am brilliant. It was kind of a weak out in terms of getting rid of Donna, but I suppose this way you can bring her back with ease. She's got a Doctor in her head. So, slowly, in her subconscious, he can work out some sort of route to return Donna to old Donna with all her memories intact.
I also like the setting up of who's the new Torchwood team: Martha Jones and that bloke Mickey. That leaves Torchwood without the tech whiz that Tosh was.