Seinfeld is very gauche but I think it was self-consciously so. The things people hate about it I hated too but many I've come to regard quite fondly (e.g. Jerry Seinfeld's bad acting and smirking). Sometimes too it was perhaps guilty of smugness regarding its own clever plotting... The self-referentiality, too, sometimes feels quite self-regarding and smug. But then on the other hand there's a sense in which all this goofiness and winking at the audience can feel quite inclusive and unpretentious, as if they're letting you in on the fun of writing/performing it. And the self-referentiality can also pay off in comedic terms. Was going to explain this by describing a scene from the show but it'll take too long and I canna be bothered.
I think another thing about Seinfeld is that, despite its immense popularity, it isn't as inviting a show as Frasier, for example, because it doesn't ask you to make an emotional connection with the characters. They aren't always likable characters (George, for example, is the kind of guy who pushes children and old women out of the way to escape a house-fire), they obsess over ridiculous trivial things, they reject women for tiny imperfections... of course, most of the characters they meet are arseholes in their own way! Which is perhaps one of the things that turns luka off - the 'small mindedness' of their perspective on the world, which is to an extent glorified or enjoyed as much as ironised. This is the same thing with 'Curb' - the way you feel, on the one hand, 'Oh, what an arsehole Larry is' but on the other 'That's what I'd say if I had the balls'. It's an uneasy relationship of empathy and disgust. And with 'Frasier, the characters have flaws, they're pompous, pretentious or stupid, but these flaws are portrayed as moments of human weakness, always overcome by human virtues like compassion, understanding, empathy.
There's hugging and sentiment in Frasier, and it makes it feel altogether warmer and more approachable in some sense than Seinfeld (although I suppose Frasier alienates many with its self-consciously high-brow references), in which there is (famously) 'no hugging' and 'no learning'. This is actually what distinguishes Seinfeld above all else as a sitcom, this moral void. In a sense its like 'Peep Show' (which perhaps counters your view of it as somehow less evolved than these modern comedies) - it concentrates on human weakness to a neurotic extent. I think human weakness is a source of much humour, whatever the moral implications of this might suggest.
Sorry, didn't mean to write an essay and I'm sure I won't convert da haterz anyway.