I have to admit that I have only seen the episode once, and that I'm a recent fan, so I didn't see it when it first came out. I remember thinking the episode was brilliant until the Abzorbaloff appeared. The monster was rubbish, and what it was there for and its story was rubbish. A rubbish monster can really throw the entire episode for me (which is why I feel that "The Time of Angels"/"Flesh and Stone" and "The Angels Take Manhattan" are terrible episodes, because the Angels are rubbish).

However, what really ruined the episode for me is the ending. It's not the comment about Elton and Ursula's sex life. It's that the Doctor locked her in the slab at all. The Doctor knows the difference between "living" and "existing", and should never have even considered doing it - it amazes me that both RTD and Tennant allowed that to happen.