There were two aspects to this story that particularly worked for me:
1) The Headhunter / Karen re-appearance almost out of the blue and acting as a foil to the Doctor / Lucie
2) 19th century Sweden - I don't know why but the cast / sounds / acting really made me feel as though I was in Sweden (and yes I have been to Sweden, but no not in the nineteenth century).
I liked the idea of the Doctor needing to destroy works of art created by an alien which acts as a backdrop to this and I think that Doctor Who as a whole would benefit from the Doctor having some hobbies and acquiring new skills rather than just having lived a long time, knowing stuff and wandering essentially aimlessly and living in the moment. Not that I think a story arc should crowd out the story you understand!