I think Fawlty Towers is possibly the most tightly written sitcom ever made. However, almost all the performances except for the four principle actors (Cleese, Scales, Sachs, and Booth) were just dismally amateurish.
I though the fellow who played the Major (Ballard Berkeley?) was pretty good. Of course, the character’s a stereotype, but his scene with the moose-head was hilarious.
Benjamin Sisko the character is pretty damn great. Avery Brooks the actor is… well… kinda special.
There’s an alternate universe somewhere where Morgan Freeman returned to television and played Benjamin Sisko for seven seasons. I wanna see those episodes of DS9.
For the record, I’m a Boreanaz-lover. I even like Blucas.
Elisabeth Rohm, however…
Olyphant’s clench-jawed and stoical Bullock is, IMO, is deliberate rather than just bad acting. The Bullock character is repressed and keeps his emotions (sometimes just barely) controlled. Remember how coldy formal he and his wife are in their relationship; they even address each other as Mr. and Mrs. Bullock. I’ve seen Olypant in other things and he has a respectable range as an actor.
In the fall, I saw Avery Brooks in Othello and I thought he was pretty damn fantastic.
Mark Harmon in NCIS. The show survives on the greatness of the other actors. Harmon and his character are awful
Well, he was a drug dealer in Go…
John Lovitz on NewsRadio. To be fair, he has more perfectly valid excuses than anyone else ever - I mean, who could have pulled off replacing Phil Hartman?? - but still.
I’ll second E. Rohm in L&O! I couldn’t wait for her to go, but I’m not too crazy about the latest assistant DA either. And the redheaded DA on SVU is easily the weakest link there.
One of the more Craptacular choices I’ve seen in an otherwise grand cast is Margo Kidder in Superman: the movie. In fact, if someone can explain her career, I would listen if it could be done in less than 30 seconds – she is AWFUL and makes Candice Bergen look praiseworthy as an actress.
And while I’m here, I just want to say, if I had to pick a captain, any captain, it would be Sisko and that is due primarily to the power and presence Brooks brought to that role. (Though if you get your hands on the Morgan Freeman DVD’s give me a holler, he would have been really interesting in that role)
I wonder in which Universe Martin Lawrence plays Sisko?
Oh, and while I’m at it, except for six degrees of separation, Wil Smith is the weakest link in anything else he’s done.
At the risk of offending Twickster who loves this show, IMO the entire cast is awful, the writing is awful. It’s a near parody of procedurals (which Twickster says is the whole point) but it doesn’t work for me.
When I saw the thread title, I immediately thought of Elisabeth Rohm. I’ve only watched one episode of Bones, but I liked it (Christmas ep). And, hey, I like Boreanz, even though his character on Bones seems like a just like Angel (aahhh…nice and familiar). I like Olyphant, too (where’s the shrug smiley), I thought he was pretty good in “The Girl Next Door.” (I really do have good taste in movies and tv, really, I do. I just watch a lot of stuff). I agree with Askia that one of things I found unwatcheable about DS9 was Sisko. I’ll contribute Alex Kingston of ER (one of the main reasons I stopped watching) and the one I’ll call the non-union Mexican equivalent of Robin Williams: John Leguizamo (however, I think he’s a guest star, and I’ve long stopped considering ER to be “good.”)
Paul McCrane as Dr. Romano on E.R.
E.R. started circling the drain when Anthony Edwards (Dr. Greene) left the show in 2002. Greene had really been the one who kept Romano somewhat in check within the storylines. With Greene’s death, Romano started running hogwild. It’s one thing to be a badass character, but Romano went wayyyyy overboard. He’s pretty much the reason I stopped watching E.R.; by the time they killed him off, it was too late.
Drew Carey on The Drew Carey Show was a pretty terrible actor. I know he was primarily a stand up comedian, at which he’s hilarious, but as an actor even playing himself he emoted like a block of wood. I contrast him with Tim Allen and Bob Newhart, two other comedians who also basically played themselves, but who didn’t strike me as people trying hard to act.
I’ve seen two episodes of E.R. - ever.
In one of them, Romano gets his arm cut off by a helicopter blade.
In the other, a crashing helicopter lands on him.
I, for one, was totally satisfied with his character arc. 
-Joe
Oohh…I hate to say this one, but…
Laura Prepon.
Fantastically attractive, and pretty genuinely likeable - but her delivery of so many lines is just…wrong…
-Joe…using too many…
The person I thought of when I saw the thread title was the person who plays Meredith Grey on Grey’s Anatomy. I think her name is Ellen Pompeo. She is supposed to be the star of this show but she is by far the worst actor in the cast. She always has the same tone of voice in every situation and always has this “ew, look at how smokey sultry I am” look on her face. I don’t watch the show because of her acting.
That’s funny…I immediately thought of Ted McGinley. But then I noticed that the OP referenced “great” TV series…
The white trash (and assorted other colors) on “Jerry Springer” are just phoning it in these days.
Except for the reluctant vote for Imperioli, who is not a bad actor, I have been scratching my head over which show I watch that has weak actors. I try to avoid such shows. There are only a few that fit the bill of being “Great TV Series” who have “Bad Actors” associated with them.
That said, I believe Janel Maloney on The West Wing gets my vote. She had some story/plot relevance back when Josh and Donna had a little spark thing going. But after her accident and then her leaving the White House to assist in the campaign for Vinnick, her character has seemed unnecessary and her job of making the character likeable unconvincing. Her whiny voice is almost impossible to understand without the Closed Captions on.