What I love about songs like “The Song Remains The Same” and “Over The Hills And Far Away” and so many others in the Zeppelin oeuvre is the different "movements" to the songs and the way they're integrated (or not). I'm sure if I went on a musicological excavation I could find other bands who did this before them, and bands who followed may have done it better, but Zeppelin had a special way of exploring multiple musical ideas within a composition.
Take “Over The Hills,” for example. The song starts with an acoustic country-blues intro. It's interesting enough, but it doesn't stay there long. I don't know if it's because I've listened to it so many times over the years and now I know better, or if they actually constructed it this way, but there's a feeling of anticipation in that intro. I listen to it and I know they're just getting warmed up, that there is something else in store for us, and sure enough there is.
What's really great about “Over The Hills” is that they don't end the first idea so much as pile something on top of it and make it work. Listen carefully and you can still hear the acoustic strumming even as the big beat of John Bonham and the vintage, electric Jimmy Page guitar take over. A song doesn't have to be one thing. There's something to be said for finding one idea and carrying it to its logical conclusion, but creativity can be messy and not all messes are bad.
The Led Zeppelin backlash sometimes gets them dismissed as being big, dumb, obvious, and clumsy (among other things), and yeah, there was that side to them, but there is nuance and texture in many of their best songs for anyone who cares enough to be open to it. “Over The Hills And Far Away” is only one of many examples.