The Mind Trap was pretty good. The start was trippy and it was a great adventure. I liked seeing the familiar story book characters (I knew that was rapunzel's hair the second he caught the rope). I did roll my eyes on how easy Karkus was defeated but the sword fight later made up for it. D'Artagnan and Lancelot were good calls by the doctor.
The Mind Robber is the actual name, though The Mind Trap is actually a better title, thinking about it!
The behind-the-scenes stuff is that episode one was added on to the existing four-part script after there were problems with the previous serial - hence the low-cost production (no guest actors, no new sets, even the robot costumes were borrowed from another BBC SF series). But it's still brilliantly creepy!