Matter of taste I suppose but there is a solidity about the first four series and an ongoing drama since Fred Mumford's parents don't actually know he's dead. Being new to being a ghost, he's clumsy so that gave it an endearing quality setting up many a farcical situation. Anthony Jackson. the guy playing Mumford decided to leave the show and the other actor, Michael Darbyshire an elderly guy died so Bob Block had to write out two main characters in one fell swoop and what he replaced it with was just pure infantile drivel.
The first series was amusing since Hubert Davenport had died as an old man but his Mum had died rather young hence his young Mum would often appear scolding him causing him much embarrassment. They got rid of that gag after then and they would have occasional guest ghosts popping in notably Calamity Kate, a female cowboy.
I guess there's lots of shows peppered throughout TV history that ended up outstaying their welcome and going on far too long hence later series tend to be a pale shadow of what came before. I can't really speak for "Most Haunted" but it does seem a formula that would be sustainable for a few series which unfortunately they then ramped up to Scooby Doo levels to try and keep it going.
Sounds a bit like "Most Haunted", ay? First few series, Great! but then a steady and sad decline into silly gimmicky trashiness. "Most Haunted" started going downhill after Richard Felix left. He cited a "Scooby-Doo" style creeping into the show and that put him off continuing with the show. He(Felix) ended up producing a series of videos where he'd travel around England, Scotland, Wales and Ireland(Republic Of, and Northern[Ulster]), talking about the ghosts that haunt the various landmark locations in the cities, towns and villages in each country. I watched them on YouTube via a website called Hunter TV(an aspirant community TV station forced to operate on-line due to bad decisions by the Minister For Media here in Australia) I think I've just about seen them all. Just as well because those YouTube vids chew up a lot of megabytes, even when they don't get downloaded to your computer but are just "streamed" to it. And those megabytes soon add up to gigabytes(chomp!).
I love the first four series of this with the original trio of ghosts - Claypole, Fred Mumford and Hubert Davenport. The ridiculous japes they'd get up to and Mr and Mrs Meaker usually falling victim to all manner of absurd spells was for me pretty funny and can still have me laughing today... and did anyone ever notice that this show did NOT have a laughter track?
When Mumford and Davenport left, we were left with the most irritating ghost Claypole and in came that damn pantomime horse, Nadia Popov and the McWitch and the show suddenly became embarrassingly infantile - worse, Christopher Biggins was present for one whole series. The Meakers and the neighbours - The Perkins - would always have great moments but even as a kid I felt it had gotten too stupid. Of course the show was always stupid, but when you cross the line to being too stupid, it can be downright painful. The final series is a complete and utter travesty.
It was strange watching them all again when UK Gold showed them in the 1990's... again, it was sad to be reminded of how it plunged downhill once series 5 comes along.
And here's a horrible fact as well as a fortunate one. In the early 90's some idiot in charge at Childrens BBC had tons of vintage kids TV shows WIPED. All first four series of "Rentaghost" were wiped when it should had been series 5 onwards that should had been wiped. Thankfully, UK Gold had recently made copies for their channel hence they all survive but had UK Gold not been in existence, then the four best series would no longer exist.