Cool question! And I had to register just to answer it. :-)
I was in 11th grade in 1982 when I first got into Zep. Growing up in the 70s and listening to FM radio I of course had heard all their hits, but at that time I was more into Peter Frampton, Fleetwood Mac and disco -- you know, the soft stuff.
In high school I got very into punk and new wave. The Clash were my main band, saw them play a bunch of times. I had an asymmetrical haircut and wore black all the time. Smoked cigarettes and hated the world. Total misfit.
One night I found myself hanging out with a few kids from school including one of the popular guys, a jock. The kind of person who normally wouldn't speak to a weirdo like me. But he turned out to be cool. We hung out on Riverside Drive in NYC, sat across from the river. It was also the night I smoked pot for the first time. Felt all funny and couldn't stop laughing. The night sky was beautiful.
Later, we all went back to the jock's apartment (his mom was asleep) and he put on Houses of the Holy. It was The Ocean that really got me. I couldn't believe how hard they played, how much they rocked! That incredible blues guitar, Plant's over-the-top voice. And Bonzo, oh my god! A bunch of us were sitting on the bed and when the end part came on, where the band is all doo-wopping, we were all singing along with the record. I knew I was hooked for life. Amidst my punk collection, which included The Clash, Sex Pistols, the Damned, Crass, etc., I added pretty much everything up through Physical Graffiti.
Like the punk bands I loved, Zep had energy. But more than that they could really play their instruments! And they were funky too. Coming from a soul background (I'm black so I grew up with Marvin Gaye, George Clinton, etc. around the house) that just made Zep the total package.
Still hooked, 30 years later. I've listened to em on vinyl, cassette, CD and now mp3.