So, yeah, it's not abfab and it's true: at first, it feels like one of those inside-joke french and Saunders sketches that go on too long. HOWEVER, this show isn't meant to be the laugh-fest that abfab was. It's a much more balanced and calm series, one that finds humor in very human situations and subtleties. This may sound far-fetched, but there definitely is a sort of Chekhovian feel to Saunders' writing. Nothing much happens, but it is fascinating to watch the characters interact. The show touches on the awkwardness of living with such truth -- and therein lies the comedy (as with Chekhov, some viewers will only read tragedy... it's really a matter of perspective). The reason it may not catch on at first is because of the time necessary to establish the characters (there are perhaps too many) and adjust to the numerous subplots (it is an extremely ambitious show, spanning many tele-genres). Because of the character development and greater humanity of the writing, the show feels more like a full TV series than Jennifer Saunders' other work, and I think it's a sign of a certain maturity on her part. The classic Saunders quirks and humor are all still there, but it's toned down to approach something more like reality (unlike abfab, it is sans a laugh track, if that says anything). So, yeah, you have to realize Jam is a different animal.
Also, you've got to give Saunders credit for assembling a fine ensemble of older woman -- a demographic that is widely ignored by contemporary TV.