Oh look. The very fine American sitcom (which never really took off here) The Middle has come to an end, and someone at Vox writes in praise of it as a very underrated show. I agree.
Regarding current sitcoms from America: have tried looking at Modern Family a few times - seems pretty awful to me. Last time I saw Big Bang Theory, I thought it had run out of steam again (after having staged something of a recovery after the silly story lines involving Howard being an astronaut.) I have also seen a bit of the revived Roseanne. Sorry, but it doesn't have the same spark as the best of its first incarnation. That actress who plays Darlene, though - she seems to have never aged.
In short, good sitcoms from the US are currently hard to find.