I was thinking about Andromeda today. Plenty of shows have jumped the shark, but that show leaped over the shark on rocket-powered skis. The first season and a half set up one of the best sci-fi mythoses of any show, and introduced us to as good a cast of characters as any show I can think of. It had the potential to be great. Then they decided to dumb the show down, and Kevin Sorbo used his clout to make his character the center of every episode. Robert Hewitt Wolfe, who had developed and run the show, left and the whole thing went to hell.

It still makes me mad to think about it.

What other shows have taken giant nosedives in quality?

Firefly. The opening credits were good then it was downhill fast from there.

Family Guy

Alias from season two to season three

24...

Also the Sopranos.
Probably jumped the shark when Junior started singing at the end of Season 3.

Star Trek, between seasons two and three.

X-Files... though it was more of a slow decline than a nosedive. It spent several years circling the bowl before it finally went down. I think it really died between seasons seven and eight, when Mulder left.

Buffy the Vampire Slayer, between seasons five and six. While I did enjoy the entire series, season six was kind of a mess.

Babylon 5 after the Shadow War ended early in season four. Sucked all of the mystery and tension right out of the series.

Rescue Me, this season.

"Roseanne". The show was slipping some in later seasons, but even so the rock-bottom of the "lottery" season was startling.

It would probably be harder to make a list of shows that didn't nosedive as they aged.

The biggest nosedive off the top of my head was Season 2 of Dark Angel. Even Jessica Alba couldn't make that steaming pile watchable.

The Shield!

The 4400 went downhill in season 2

24. Went from one of the best seasons..to a horrible crapfest.

Commander in Chief..started out so well..then fell apart.

I think I might be the only one. But I think as a whole, season 8 was stronger than season 7

season 9 was a crapfest however.

24:
Looking back, after the show's best season (Day 5)...who knew giving Kiefer and Co. an overdue Emmy would result in one of the biggest brain farts in television history.

Roseanne and that final "lottery" season is a close second.

Let me throw in the obligatory Simpsons post (somewhere around S10).

Happy Days.

Pretty much around the time that episode aired where Fonzie jumped the shark tank.

I thought season 2 of DA was a vast improvement.

As for going bad:

Millenium season three, after the great season two.

Gilmore Girls, sometime after season three. Four was okay, but but by five I stopped watching.

Dark Angel - Season 1 was very good, the premiere episode of Season 2 was also very good, then it went from enjoyable to completely unwatchable by the 3rd episode.

Grey's Anatomy - immediately after Denny's death

Dead Like Me

Agree with Sopranos

The O.C., by a wide margin.

I have to agree. It completely tanked from the start of Season 2 on.

When I saw this thread, I thought that it would be about Rescue Me this year.

By far Lost S2
followed by...
Prison Break S2
24 S6