TV show dynamics

Ever watch a TV show and notice that the quality from episode to episode depends heavily on certain characters being included and relationships between certain characters being present ?? … Here are some examples …..

One of the biggest examples of this is The Wonder Years …. the very essence of this show was Kevin and Winnie …. if the episode was not about their relationship it felt like a completely different show …. this series depicted the up and down on again off again relationship between main character Kevin Arnold and his love interest Winnie Cooper very well …. and realistically as everyone of that age could identify …. but when the show did not have Winnie in it it felt lacking …. stories relating to Kevin and his immature older bully boy brother …. that guy should have been around for a Rockshore commercial !!!! …. or accompanying his father to his workplace or to buy a suit and get lost or Kevin going to some mildly smutty film with his pals etc never piqued the interest for me that Kevin v Winnie did ….

Another example is the one off experimental episode of 1980s classic Miami Vice called Leap of Faith …. Miami Vice was at its very best when Crockett and Tubbs plus the other regulars were in it defeating drug dealers …. this episode did not feature Crockett and Tubbs much at all and none of the other regulars …. just a cameo of Crockett and Tubbs at the start and was all characters either not at all or seldom seen … one was a minor undercover cop character introduced in an earlier episode … in MV …. MV was all about Crockett, Tubbs and their dept …. not some random new cops …. thankfully Leap of Faith was only one episode though !!

Midsomer Murders …. here is a one though that changed the lead character …. when Tom Barnaby was the main character it felt right …. once he was done it was not nearly as good imv ….

What other series come to mind where the main characters or certain dynamics define the best of the show … and things suffer completely when they are absent ?? ….