This is one I remember watching in 2009 with my little brother. I'm not sure we knew 100% what was going on with the notoriously complex plot back then so this time I had the subtitles on and was in full concentration mode. I watched the originally transmitted version, not the newly expanded ones that Marc Platt recommends (I would be interested to see these).

At its heart Ghost Light is two plots which have been smooshed together. 1) Haunted house from Ace's childhood gets a backstory (great!). 2) An alien surveyor from eons ago wakes up after a long sleep, pissed off to find that his survey is out of date (mmm... okay!) The first of these two elements works like a charm and is sufficiently affecting that the huge amount of intricate detail you have to take on board with the surveyor elements gets a pass. This would have the potential of being McCoy's best story if it had just been simplified. The Victorian setting is always perfect for Doctor Who, this plays well with the increasingly mysterious nature of The Doctor and Ace's growing backstory. Ace feels like a real character.

Josiah Smith is a good main villain, though I'm not sure why he was "evolving" into a Victorian gentleman or taking over the house. I enjoyed The Doctor trying to teach Light of the futility of opposing evolution though - that felt very "Doctor-ish".