Why do you need The Complete Seinfeld? Among other reasons:
* It's the canonical 90's TV show, even moreso than The X-Files and Twin Peaks and (yes) The Simpsons. In terms of both sitcom history and recent American cultural history it's an invaluable resource.
* There haven't been many comic ensembles in the history of television with the chemistry and chops of Seinfeld's cast. Even the group's weakest actor (Seinfeld himself by a large margin) was blessed with great timing and a natural feel for how to deliver a punchline; as the show developed according to each performer's strengths, his comfort and ability grew, and by the show's fertile middle period he held up his end of the show just fine. His castmates, meanwhile, are masters who deserved every Emmy.
* While it's been surpassed in this regard by Arrested Development, mid-period Seinfeld featured the most complex sitcom plotting yet seen, not to mention the darkest outlook of any network comedy I know of. It was poisonous satire played skillfully to the cheap seats, written with the dense referentiality of The Simpsons. The best writing on Seinfeld was the smartest and funniest on TV, Back Then.
* Why in the world would anyone forgive Michael Richards anything? Because Kramer is one of the great TV roles - a type and yet an individual, which is to say an icon. George is a richer role, Elaine a more difficult one, but of the four Kramer is the holy figure.
Bah. I just bought the thing while writing so I'm fresh out of ready-for-sublimating desire. Just buy the damn thing. $99 is a fantastic value for this much TV.