The title of this set of Episodes should be "Carry On Clantons".
Yes, this is the worst Dr. Who episode ever. That makes it an absolute must-have for serious Dr. Who collectors. The entire episode is played for laughs, and probably seems funnier to a British viewer than to an American. Listen closely to the lyrics of the background ballad - it's a "bang on" parody of 50's America western background ballads (think "High Noon" or "Gunfight at the OK Corral"). The cowboys with British accents are hilarious.
ON the downside, there is very little actual conflict or suspense in the story line, and too many of the jokes are predictable or downright lame, at least to an American sense of humor. But for the Dr. Who enthusiast, it's worth at least one viewing.