Good article. I've thought a lot about what exactly is responsible for the incredible appeal of Zeppelin. I'm one of the under-25's who discovered them one day and got hooked. For starters, they just reek of rock and roll. So many other "rock" acts have descriptors in front. Punk rock, alternative, metal, southern rock, progressive rock, arena rock, grunge rock, blues rock, etc. If you had to explain the concept of "rock" to an extraterrestrial by playing one album, what album would be more appropriate than one by Led Zeppelin? (I'd choose II)
They have an aura of authenticity about them. They weren't commercial. Their albums have no "filler". I can identify a Zeppelin song instantly, even if I've never heard it before. It's heavy. It sounds like its being played live.
I guess it is hard to put my finger on it, but no other act even approaches Led Zeppelin.
Led Zeppelin is one of the few bands that can be recognized immediately even if you haven't heard the song before. Very few bands have that today. Red Hot Chili Peppers do, and Audioslave do but not many others do.