Started with a boring 35 year old Cop, pissed off that Aliens murdered his wife who was lozenged into a vat and preserved, who was replaced with the best bad guy's magic half alien baby with super powers who grew to maturity over night and instantly went to the mall and got frosted tips, who sacrificed himself to save the world, just like Jesus, who was replaced by a girl version of Tony Stark who looked a lot like my mum, blond and booby.
Shelley Long and Ted Danson were co-leads, he was not the main star or more important than her (also shown in how they were credited, they shared a screen in the opening, his name was on the left left but hers at the top so that they were on equal footing, he came first reading from left to right but she came first reading from top to bottom) and Danson himself is on record saying that she carried the show in the beginning and put it on the map when he didn't really know what he was doing and he also credits her with being cast in the first place, they were paired early during casting when they tried out different Sam's and Diane's and according to him Long was so good she basically carried Danson through the final auditions.
Actually seems to have done it a great deal of good. Potter and Hunnicutt were much more rounded characters. So, for that matter, was Winchester, when Burns was written out. The characters who lasted the entire run did so because they evolved.
