TV shows replacing major characters with similar characters

Makes sense from a writing perspective, doesn't it?  No need to change the dynamic between characters, and the audience should immediately feel comfortable with the clone character.  And yet, in my experience at least, I always found such a situation unsatisfying.  "Three's Company" replaced Chrissy Snow with another dumb blonde (Cindy), one who was Chrissy's cousin, to boot.  Yet the show only rebounded when the very different character of Terry, played by Priscilla Barnes, joined the cast as a permanent replacement for Suzanne Somers.  "Alice" replaced the popular Flo with another southern "Belle" played by Diane Ladd, who had actually played Flo in the movie 'Alice Doesn't Live Here Anymore.'  Belle's addition to the show proved a misfire, probably mostly for behind-the-scenes tensions, but I'm sure many fans of the show, unfamiliar with the movie, felt like they had had the understudy foisted upon them.  

Are there any shows in which you prefer the very similar replacement for a departed main character?  Have there been any clone replacements that you found particularly unsatisfactory?