Not a sitcom per se but i was always very partial to Richard Briers' Oneupmanship - a 70s series that extended the concept of School for scoundrels (Terry-thomas, ian carmichael) in which Briers demonstrates in various sketches how to get one up in any given situation. One i recall was about how he got a big sit-on tractor mower to do his lawn and drove the man next door insane with jealousy. When the man spent a fortune buying one to match, mowerman says Oh Im just taking this loaned mower back, i could never afford a beast like this" - thus getting one up on neighbour coz he'd been out and spent loads!
There was a 2013 TV series on Channel 4 in the UK called The Mimic that I really liked. It was a quiet, slow and unassuming show that was contemplatively off-beat. Well worth checking out.
Jim, did you ever carry on with How Not To Live Your Life?
I started to, and I enjoyed the little I watched. However, the episodes on the 'Tube can't boast the greatest audio and video fidelity. The sound is slowed down and the picture is crunched into a wee box. I've watched many ancient VHS SLP recordings that were better presented than this. I am on the lookout for better versions, though.
Fairly Secret Army is brilliant. Series one definitely has a deadpan John Cleese-ian touch about it. I especially like Geoffrey Palmer's "conversations" with "God." The humor is mostly of the subtle variety, and I love it.