Indeed, different strokes for different folks. I liked it, but not always - like most comedies there are good and bad moments or characters but you tend to 'take to' the overall vibe or not.
Yes, the musical was mentioned in that documentary - something to do with Paul Whitehouse I think (who was also one of the talking heads).
In the US they milk it for much more - more episodes, plus several seasons. Think of Fawlty Towers and The Office (UK), 2 seasons of 6. The American version of The Office has god knows how many episodes. Friends ran for a decade with 20+ eps per season, and The Simpsons is still going! It's not a good or bad thing but probably down to a team of writers (as you say) rather than a couple…