I can go on about what makes Seinfeld what it is... one of the most revered TV shows in history.
1) Originality. The show's concept was highly unusual for the early 90's. The show had no point to it. No goal in mind, no hidden concept. It was a show about everyday life. Or a show about nothing. The writing was true to life, and the actions of some of the characters are realistic. In most sitcoms, you'll find a sense of theatrics when things happen. Not with Seinfeld. Anything you seen on there could happen in real life.
2) It's an underdog story. Many think that Seinfeld was always where it is now. Not the case. The first season only lasted 9 episodes due to it being a mid-season replacement show. The ratings weren't that good and some of the acting wasn't up to par either. The second season is where it got some of its legs under it, but it was still struggling. It wasn't until the third season that Seinfeld hit its stride as a great TV show. Many shows are good from day one. Seinfeld wasn't. Yet, it went on to be the most critically acclaimed show in TV history.
4) It's place in popular culture. The sayings, the characters, the lines are all apart of pop culture to this day. I still use "Yada, Yada, Yada", "Giddyup", "It's not you, it's me", and other random lines from the show. "Mimbo" is my fave. Male bimbo. lol. Even though some may not like the show, it's still respected as a well-written, sensible show. Most don't get the humor. And that's fine.
But to say that it's inferior to a Nickelodeon show that was nostalgic as a kid is absurd. But it IS a popularity contest. And that's fine. But know that Seinfeld should move on, and if it does... it'll beat any show in the tourney. Past and present.