The first song of the first Led Zeppelin album. This is about as perfect a mission statement as any. The Beatles kicked off their whole show with "I Saw Her Standing There." Jimi Hendrix entered with "Purple Haze." The Doors set things up with "Break On Through (To The Other Side)."
Radiohead greeted the world with "You." See, we can't all score on our first drive.
For their first number, Led Zeppelin decided to courteously announce to the world that, for the next decade or so, music would fall under the fiefdom of one blazing guitarist who happened to be the Beethoven of riffs, one shrieking blues-singing vocalist who could do things that no other mortal could do, one sickeningly smooth bassist who could run scales for fortnights, and the most consequential drummer of all rock and roll for all times.
It's hard to pick an MVP in the song, so balanced as it is to be a show piece for all. However, I pick bassist John Paul Jones, because those bass runs in the second verse are so mean, and where did this school of bass playing go?
Formally, this song has a novel feature: An A-verse, a B-verse, then returning to the A-verse after the guitar solo. The A-verse is built on a catchy major blues phrase that both guitar and bass play in unison. In the B-verse, the guitar shifts to power chords while the bass is the feature instrument in minor blues. In a world where verse/chorus/verse/chorus is abused and exploited with breathtakingly little remorse, I have no idea why the "Good Times Bad Times" form isn't more widely used. It takes a little more work to come up with a related but distinct B-verse, and maybe that's the deterrent, but it strikes me as a great way to avoid repetitiveness. Third verses are also growing more rare. Maybe because of this feeling of repetitiveness. Maybe people just don't have patience for three verses regardless and the time for A/B/A verses has passed.
Finally, for what it's worth, the singing melody never repeats across all these verses - there is new concept for each one. The kitchen sink mentality of the whole song pays off when you're dealing with a drum beat and music ideas this fun and catchy.