The Mind Robber is unique and interesting and also one of the few surviving Patrick Troughton stories. It was written by a man unused to doing science fiction, but good at writing children's fantasy. It's quite well known for a number of reasons, including a certain scene with Zoe and Jaime having his face rearranged so he could be out for a week due to illness. Always keep in mind the early serials were heavily tied together so it will start and end with an unanswered question, though it does have a conclusion in the final episode. I must advise watching the special features to learn more, and to enjoy all that they went through working on Doctor Who. Troughton was a great man and a great Doctor, and like Wendy & Frazer say, we will be dearly missed. Bernard Horsfall who makes an appearance also shows up in several other stories.
This was a good story for meeting the characters, Jamie and Zoe, Jamie is from the past; think of the time and place of the movie Braveheart. Zoe is from the future, a time when space travel will be common, and we will presumably be wearing shiny outfits.
This is a fun plot with the Doctor and companions trapped in a dimension where fact and fiction are blurred, and they are themselves in danger of becoming fictional characters.
Entertaining, if a little silly, adventure in which the Doctor encounters a world where fiction becomes reality. Also worth seeing for the first episode, where the TARDIS lands in a void and weird stuff starts to happen.