"The Alternative Factor" suffered a lot of backstage problems. The actor originally hired as Lazarus failed to appear on the first day, saying he forgot, resulting in the studio and/or production filing a grievance against him with the Guild. Robert Brown had to be hired at the last minute and the already built costume refitted. Then there's a questionable change in the script where a love story subplot between Lazarus and Lt. Masters was cut entirely because they'd hired a black actress for the role and were worried about offending parts of the United States.
I did not know any of this. Very interesting and explains many of the episodes faults.
I enjoyed the episode, and all of TOS really. The only Star Trek I did not like nor could I watch much of at all was Enterprise and Voyager.