Well, there's also The Tenth Planet
, but you mentioned seeing this already.
I continued watching season 15 and completed Image of the Fendahl
and The Sun Makers
The first one starts off in a really intriguing way, with a human skull that predates the first hominids. Though I'm not an anthropologist, as an archaeologist this excited me. The first two episodes are done really well and end in great cliffhangers. After that, the story falls apart somewhat and becomes a bit of a mess. We get treated to a ridiculous looking monster which we're supposed to be afraid of but which can actually be severely weakened by salt and is ultimately relatively easy to defeat. The minor characters, especially the old lady and her son, but also the scientist, were quite well depicted and entertaining.
I liked The Sun Makers
much better - maybe due to the sci-fi setting. The concepts of artificial suns, a megacity spanning large parts of a planet, living underground and on several levels (in a reminiscence to Metropolis) and an almighty evil corporation appealed to me. Also, we get to see Villa from Blake's 7
(well, kind of - but it could be him). The way the villain disappeared at the end looked a bit silly but all in all a good story.
Also, the Doctor seems to have taken up channeling William Hartnell by often saying, "mmh?". Or maybe I just didn't notice that before. Anyway, I like it.