I mean shows that started well and decayed into horrible shows. I actually don't mean shows that had a bad finale, but were otherwise OK. What shows degraded the sharpest in your experience?

Very good to excellent programs that have multiple unwatchable seasons at the end:

Andy Griffith Show
Bewitched
MASH
Happy Days
Cheers
The Office

Drama: House, MD

I think I recall that original-recipe Hawaii Five-O decayed in its last couple of seasons (1978-80).

The Simpsons

The Andy Griffith Show, The Brady Bunch, Laverne & Shirley, Happy Days, Sabrina the Teenage Witch

LAVERNE AND SHIRLEY definitely and GIMME A BREAK (yikes--that New York, Lawrence-heavy season) and THE FACTS OF LIFE as well. Also PETTICOAT JUNCTION flew off the tracks after Bea's death so the last few Kate-less seasons are somewhat poor and forgettable.

Also PETTICOAT JUNCTION flew off the tracks after Bea's death so the last few Kate-less seasons are somewhat poor and forgettable.
I agree. I still like the later seasons of "PJ" but without Bea, they left a lot to be desired.

Laverne & Shirley
The Andy Griffith Show
The Brady Bunch
Happy Days

Roseanne

-Family Matters
-Happy Days, esp. when they stopped caring that the characters were wearing early-80s fashion

night court empty nest ghost whisperer

Happy Days, Laverne & Shirley, Hazel (last season), Green Acres, Mr. Ed (last season with the "spy" episodes), Taxi, Bob Newhart and Newhart, Good Times.

Happy Days owns this thread. Also, Bewitched post-Dick York and Andy Griffith-post Don Knotts.

Diff'rent Strokes
Family Matters
Scrubs

To name a few.

Ed.

The Simpsons

Agree...

Will this show ever end? The 90's WAS The Simpsons, now they'll just keep the show on because it's a cash cow!

The best examples of this for me are Happy Days, Bewitched, The Office, and Roseanne. Modern Family is on its way to joining that list, too.