There's also a series it was based on, ("Secret Army"? "Secret War"? Something Something Resistance"?) that everyone (OK, me) had forgotten about or never seen. Mildly ironic that the pastiche of it went on to be far more famous and long lasting than the original. I saw a bit of it once and it had the resistance lady in the raincoat saying something very close to "pay close attention I shall say this only once".
I'd argue it's the period setting too. It won't age as obviously as other comedies as it's set way back when. The same with Dad's Army.
'Allo 'Allo is wonderful. Really brilliantly funny, in a way that hasn't aged at all.
Edit: to clarify, it works because it's the 'in on the joke' style distilled to almost too much a formula. In that respect it's The Fast Show a decade early. There are no characters, only caricatures and everyone knows what to expect whenever they see any of the cast enter a scene. It's closer to a farce than a sitcom. It doesn't all work (Leclerc isn't that great and it goes wrong when they recast the Italian captain) but the fact they could construct an episode entirely from catchphrases and still make it work makes it something wonderful to watch for me.
Watch the pilot again, you'll be surprised.
Anyway, Allo Allo was terrible, but quite good terrible. Dad's Army can fuck off, but if they want to show some sort of heavily edited meta-episode of clips where John le Mesurier is being calm and suavely superior interspersed with occasional cuts to Arthur Lowe making harrumph noises or looking harrassed I'm pretty sure I'd watch all 30 minutes.