They stuck with the 65 episode series so religiously that when the show was popular and they wished to make more episode, the series would be retitled, with the intent to fill out another block of 65. Thus the third season of Gargoyles was titled originally Gargoyles: The Goliath Chronicles.
I don't think that's quite right. The show moved from daily syndication to Saturday morning network airings after season 2, and it was retooling by the network that led to the changes in story and title. There was no reason to retitle a series if it got another 65-episode season; that was simply the length of a single season (13 weeks x 5 days a week), and if a series got renewed for a second season, it would get new episodes without a title change (see
He-Man, She-Ra, DuckTales, The Real Ghostbusters, Ninja Turtles, and countless more). I think you're confusing the '80s/'90s practices with the modern policy of Cartoon Network, which seems unwilling to let a series go more than 65 episodes without either cancellation or retooling. But under modern cable practices, with weekly rather than daily airings being the norm, 65 episodes means 2.5 to 5 seasons, when back in the day it would've just been one season (or two seasons, if the show started with a 13-episode weekly run and then got 52 more to fill out a strip-syndicated schedule block).
What is everyone's thoughts about Season 3?
Why is it so hated? Is it worth watching once, or should it be avoided at all cost?
As I said, the show moved to Saturday morning network airings for season 3, so it fell under tighter restrictions and pressure to target a younger demographic. It's much the same thing that happened to
The Real Ghostbusters when it moved from syndication back to network -- the episodes got less adult, less sophisticated, more juvenile. Also, Greg Weisman, the showrunner and principal creator of
Gargoyles, left the series after writing the first episode of
The Goliath Chronicles. The writers who took his place abandoned his plans for the series, telling simpler, younger-skewing, more episodic stories that didn't handle the characters or the world very well. It just wasn't very good, certainly not in comparison to the brilliance of the first two seasons.