Ah, yes, I watched a few more myself, in the meantime, and have a new favourite in "Bless this House" which, to me, felt a lot just like a longer episode of the TV series, and I guess that's the best we could expect from this kind of stuff.
It was a bit weird seeing different actors in some of the main roles, but Peter Butterworth was probably a better Trevor than the original, while Robin Askwith as the son felt a bit odd, not because he wasn't good, he was, but because he'd been a guest in a recent previous episode in the regular TV series, playing a friend of the son, and that could be seen as a tad confusing...
I also rather liked "Whoops Apocalypse", despite the excessive Americanization of the plot, but the guy playing Kramer in Seinfeld (can't be bothered to look the name up right now

) was brilliant as the killer, even better than John Cleese in the original (and that's saying something, for me

), while Peter Cook as the PM is still regarded as his best performance ever in a "pure acting" role.
I wonder, however, if this film fits the bill, here, being the remake of a mini-series rather than the "spinoff" of a sitcom...
I guess we watch the two things with different attitudes, with a remake comparisons with the original are more immediate, because it's the same plot, while with spinoffs we check the new plot against the series, seeing if it measures up, or, as often happens, it's just a "stretched" episode that doesn't gain much from the longer time-slot allowed, if it doesn't actually suffer from it.
I think that's indeed where most of the quoted titles succeeded, the longer time was usefully employed, rather than wasted.