Strangely, we don't have a thread on this story yet.
It's often mentioned and praised, and now I've finally seen it I can say... it's very different from the rest of Doctor Who (and feels odd when you compare it to the likes of Black Orchid or Earthshock!). It's one of those layered, thoughtful stories which only explains half of it and has lots of intellectual themes (like Warriors' Gate or The Curse of Fenric). But it works quite well as a normal story too.
The acting's absolutely brilliant in it - except Matthew Waterhouse - as there's lots of great guest stars. The jungle set was built in the studio so it never feels quite convincing enough (see also: the very clean forest people, the snake - which isn't that bad). I've heard it described as more of a stage play and it does feel quite theatrical... I kept thinking that there was too much cutting involved, and they should have had longer scenes rather than jumping between two different situations all the time - but that's only minor, and probably shows that I was captivated by it.