Between a 4 and a 5 for me. Been looking forward to reading this one, to see how well nostalgia held up - I only read this once or twice many years ago when was available from the library, and only recently managed to get my hands on a copy.
I think it still held up pretty well for the most part. It is a longer length than normal, which really helps build the slow creeping tension and horror for this story, as really does feel like a horror sort of tale, unusual at this stage of Doctor Who.
The enemy as such is quite a different one, but the way it gradually increases it's threat is portrayed very well, and the various other characters in the tale for the most part are quite fleshed out to help sell the tale as well, though some of their decisions did seem a bit ludicrous.
Particular scenes, like going down to the main pipe line, were really chilling I found, and described really well, and could imagine what it would be like on the big screen (unfortunately haven't had the opportunity to see the animated version, and too young for the original :( ).
The Doctor in good form as well, and while Victoria was somewhat more of a Damsel in Distress again, it actually formed part of the story, and led well to her exit, which was quite an emotional one. I've mentioned previously how the connection between Jamie and Victoria from Evil of the Daleks was just dropped, but it seemed to be picked up again here, mainly in the finale as Victoria opts to leave, and seeing the two of them navigate this was a very moving passage.
What detracted a bit from the story, was some very unnecessary commentary on the other female characters' appeal - it is fair to describe what a person looks like, and was done reasonably with the men, but what wasn't done with the men, and didn't need to be done with the women, was commentary about how attractive they were, or how they could be more attractive. Without these bits, would be a straight 5 star.