11. First Doctor - The Gunfighters (1966)
This four-episode serial first aired during William Hartnell's final season as the First Doctor. Up to this point, the show was going pretty well: it had already introduced the most famous Doctor Who villains of all time, the Daleks, and had already featured them in 4 earlier serials. Also, the show had struck a good balance between science fiction adventures in one story, followed by a historical adventure in the following story. Until this. It begins with the TARDIS landing in Tombstone, Arizona, USA, and it turns out they've arrived just in time to be caught in the middle of the infamous fight between the Cochise County Cowboys and Wyatt Earp and his men. In other words, the Gunfight at the O.K. Corral. Up until now the story actually sounds rather interesting: Doctor Who blends surprisingly well into many historical events, but this one just fails miserably. The problems begin when you realize how historically inaccurate this story is, not to mention that the episode features a subplot where the Doctor is mistaken for Doc Holliday (get it?), and of course, the singing. Oh, I didn't mention that yet? This episode is a musical. Strike three.
If You'd Like a Good William Hartnell Story: Try the Dalek's second appearance "The Dalek Invasion of Earth" or his final appearance in "The Tenth Planet".