I hate it when I enjoy watching a TV show regularly, and the producers suddenly decide to add horrible, new, regular cast members. A perfect example of this is Frasier. I liked the show originally, and continue to watch the re-runs. But I cannot stand to watch a single episode which features Daphne’s family members, imported from England (brother - Simon, and her mother - Gertrude Moon). On another old series, Star Trek the Next Generation, I hate watching every single one of the 8 episodes which feature the character Q. And on Andy Griffith, I turn off any show (6 episodes) starring the Mountain People, also know as the Darling family.
Moonlighting with Curtis Armstrong.
Bones. Sunnie Pelant and the Booth daughter. Possibly the worst child actor ever. And that includes the kid that played the young Anakin Skywalker.
Bellamy Young on Scrubs. I get the feeling they were trying to make a female counterpart to Dr. Cox (didn’t they already have one of those?) and the end result is that she is just hateful for no reason at all. Thankfully, they dropped her storyline pretty quick.
And I agree that Daphne’s family on Frasier was pretty bad.
That Seven fuckass on Married with Children. Luckily the actor got fired after one season and was never seen again.
Wasn’t Cousin Oliver pretty much the poster child(ha!) for this?
Heh. I was going to mention Seven and Cousin Oliver. 
Little House on the Prairie kept adding kids to the show.
When the oldest son left My Three Sons, they added a new “son” when they adopted Ernie.
LOST kept adding people.
There was a second season of HEROES.
Since the topic is poor cast choices, I’d say any show Ted McGinley was grafted onto…except for Married…With Children. He was an anchor during the final seasons of The Love Boat as “Ace the Photographer”, and the incredibly straight-laced teacher “Roger Phillips” on Happy Days. The man is a virtual poison-pill to any series.
The thread title says good TV shows.
Diana Muldaur as Dr Katherine Pulaski on ST:TNG
Having a crotchety doc with an acerbic wit worked in TOS because DeForest Kelly was just that good with his character. Trying to bring on the same type of character in the new series just reeked. Early TNG had many issues, but watching Doc Kate fall down an open turbolift shaft would’ve solved a couple of them.
Rosanne’s mother and all of Seinfeld’s and George Costanza’s parents. Spoiled lots of episodes. Parents are usually fatal distractions in sitcoms, turning geat comedy into inane slapstick…
OTOH Poochy worked out just fine.
Q was in TNG from the very first episode.
Disagree. Frank was one of the best characters on Seinfeld.
Kirby and Lana on Frasier.
Michael Imperioli’s character on Law and Order.
Well, there you go. In my opinion, you just proved my point.
Ron Carey (as Levitt) in Barney Miller was terribly inappropriate for the remainder of the original cast. James Gregory as Luger was also disappointing in his irregular appearances. Both were not part of the unit at all, and just wandered in and out, to no effect.
Summer Glau. She was good in Firefly and the Terminator series, but pretty much derailed anything else she showed up in.
Chandler’s screechy sometime-girlfriend on Friends. Nails on a chalkboard, I tells ya.
Agreed as to Daphne’s mom on Frasier. She really was odious. The rest of her family, I didn’t mind so much.