Norman Greenbaum > Robert Plant I don't really care for Zep, I think a bunch of their shit is overrated. Excellent for their time, but more than a few decades have past, it's easy to see why they aren't THAT great. Robert Plant solo is fantastic, though. Loved, loved, loved his album with Allison Krauss. Pretty stoked to see him with his Band of Joy at Bonnaroo this year.
I love them. And for me they've haven't really been bettered since as far as straight-up hard rock is concerned so they still have their place.
Jimmy Page is fucking overrated as all hell, but my god, John Bonham is a sort of talent I don't think we'll see ever again. Fucking tragedy.
I love Page's guitar work period. Overrated or underrated I really couldn't give two fucks. I like Led Zep and have the lyrics to Stairway to Heaven on my bathroom door.
Overrated as a guitarist, I'd agree. His playing on stage in particular has always been rather sloppy. I've always thought Page was an incredible composer/arranger though. He did stuff with guitar overdubs/multitracking that was WAY ahead of its time (The Song Remains the Same probably has about a dozen guitar tracks in it). Zep and Black Sabbath are typically credited as the godfathers of heavy metal, but the recording techniques were totally different - the early Sabbath albums rarely had any overdubs except on Tony Iommi's guitar solos, but Zep's arrangements were massive, and that's largely due to Page's involvement. Bonham and Jones were really the gems of that band though. I think other than John Entwistle, JPJ is the best hard rock bassist ever (and a hell of a talented musician in general).