Successful TV show recasts/replacements?

What shows do you think successfully pulled off the recasting or replacement of a major character? Even if the show continues on successfully, the chemistry on the show usually changes and risks alienating fans.

No soap opera's, please.

My choices:

CHEERS - Kirstie Alley replaces Shelley Long. I know people will argue but I think the first couple seasons with Rebecca really breathed some freshness into the show. It still went on way past the sell-by date but they definitely earned a few more seasons with the recast/refocusing of the stories.

CHARLIE'S ANGELS - Cheryl Ladd replaces Farrah Fawcett. Fawcett may have been iconic, but Ladd was so cheesily of the 70's that I actually like her seasons better than Fawcett's original. Now, once Kate Jackson left the show went into the toilet but for 3 seasons it was pure cheese ball, jiggle magic.

I like Mr. Furley better than the Ropers on Three's Company.
I like the second Darrin better on Bewitched.
You can't really credit it to any one recast/replacement, but I like A Different World much better after Lisa Bonet left.
On Mama's Family, Bubba and Iola were better than Aunt Fran, Buzz and Sonja.

Sarah Chalke replaced Lecy Gorensen on Roseanne as Becky. I liked them both, but I do think that Lecy's Becky was definitely the meaner of the two. Sarah played the character as much more mellow.

I guess M.A.S.H. did all right even after McLean Stevenson, Wayne Rogers and Larry Linville left. My Three Sons replaced William (Fred Mertz) Frawley with William Demarest. As much as Coach was a great character, they didn't miss a beat with Woddy Harrelson. NYPD Blue survived after David Caruso left.

I preferred Kirstey Ally to Shelly Long on Cheers too.