It's just the attention to detail. The little things. That's the real key to a great show. It lets the viewer feel more apart of it. If you're just presenting a show, then you're just presenting a show, the viewer isn't totally affected by it. But when you put little things in their, like real-life quirks or references, it gets the viewer involved, it gives them a sense of "Hey, they're dealing with something I know about it", it makes them feel apart of it. The shows storyline itsself on paper isn't too great. It's the spices thrown into the soup that give it the real flavor.
For example, Elaine and Jerry are talking. Elaine walks into the other room, the phone rings, Jerry picks it up. It's a telemarketer asking Jerry if he would like to try/order something. Jerry says "Yes" in a polite manner, then slams the phone down, then goes on talking to Elaine. Completely unrelated to the story, yet still one of he funniest things in the episode. Who hasn't been rude to a telemarketer? It just makes you connect with characters more.
For me, whether it's movies,TV, or music, what makes me connect and really love something, is that you can tell theyre having fun. They're not delivering their lines with monotone voices, basically phoning in their roles. They're really into it. You can see it when they raise their coffee cups to hide their laughter after a punchline, or when you see a sly smile slide across their face before they deliver a hilarious line. They love what they're doing, which makes it easier to love it as well.
Everything isn't for everybody. You probably just don't get Seinfeld. You may be just not be watching the right episodes (The ones on TBS right now are kind of the earlier episodes, like in the first 2 or 3 seasons, where the plot was kinda weak and Jerry's apartment was uglier. I think these are the worst of the bunch, but they're still occasionally funny nonetheless.) . Personally, Seinfeld is the greatest show ever created, bar none. It's got everything, and then some, and you don't feel left out, because every episode starts fresh, ansd there's rarely an episode related to the other, asides from boyfriends/girlfriends, or other recurring characters like co-workers, people in the apartment, etc. You can jump in and out any time. Yet, when you're in, you still feel connected, because of the little things, and because it's clear how much these people love what they're doing. If you just gave me every episode of Seinfeld to be only thing I could on TV watch for the rest of my life, I'd probably be fine with it. It's just that good to me.