I was shown Seinfeld by an American who couldn't understand why us brits didn't even get to see it - as it was stuck on in the middle of the night on BBC2. So many Seinfeld-isms have entered regular language in the States complete Seinfeld knowledge is regarded as a given, and as the humour is very 90s a bit passe. Whereas here in the UK I think it has cult status almost, as so few have seen it let alone appreciated it. Maybe the best way to view it is as a proto-Curb Your Enthusiasm. So if you like curb its very likley you'll like Seinfeld. It is very useful to have a New Yorker around to explain the in jokes.
I like Seinfeld because all the characters are so shallow! And they take the piss out of themselves brilliantly with the pilot sitcom.
What I have found here is that no one has seen it, and so you see somthing and say 'ohg thats just like in Seinfeld' and the other person says 'oh I never watched it' and then you say 'well there was this episode where..' and yadda yadda yadda you've ruined an episode for someone if they ever see it, the joke is dead and everyone feels quite tired.