NBC put the show on at the worst time-slot of the week, 10pm Friday Nights. Roddenberry left. And Fred Freiberger stepped in. Freiberger's attitude towards the show was that the show was serious drama, and therefore he removed some of the humor. What humor remained tended to be more corny and less real. Add into that some bad production values (right down the costumes, which while it seemed a necessity to change from velour to polyester, the polyester just looks cheaper in my opinion)...you get some problems.
I have personally changed my tune on this third season, it isn't as bad as I remember, but it isn't without some definite issues. Still the show couldn't be saved at this point, and it was given the definite axe.
NEXT TIME: The Whole Series Recap