Okay, I haven't read all 102 prior replies but I'm pretty sure I'm in the minority on this one: I think Robert Plant's singing nearly ruined Led Zeppelin. Arguably the best drummer in rock, the absolute riff king bringing the tonnage on lead guitar, perhaps the most underrated bassist ever and...Robert freakin' Plant, squealing and caterwauling over the top. Some Zep songs are so great that Plant couldn't ruin them, but he always tried. When I was a teenager my friend offered me tickets to see Zep at the Garden and I turned them down, as I couldn't bear to listen to Plant's screeching. (Kind of regret that, as they filmed the show for The Song Remains the Same.) Still, Zep were great despite, not because of, Robert Plant's voice. And don't get me started on his idiotic Viking/hobbit/citrus fruit lyrics...
We are a party of two when it comes to his screeching. Honestly I only like the rhythm section of that band.