Well put Electrophile. Zeppelin and Floyd are on opposite ends of the musical spectrum, but I am one of the those who loves and appreciates both. I absolutely love their early era, 1969-71, and I have a ton of live recordings from that time and their musicality is the draw for me. Songs like Set The Controls For The Heart Of The Sun, Cymbaline, If, Green Is The Colour, Fat Old Sun, Echoes, Embryo and Careful With That Axe Eugene are stellar moments always.
Once they achieved world wide success with Dark Side they were still able to write amazing music, as evidenced by Wish You Were Here, Animals, The Wall, The Final Cut and Division Bell.
I find it sad that after all these years one gets the feeling that Roger Waters regrets leaving the band. How much further could they have gone had they remained intact? The lyrical genius of Waters, combined with the musical brilliance of Gilmour and Richard Wright allowed that band to scale heights few others could claim.
Their music is on an extremely deep level... it really requires the listener to think... and to me, that is a very cool thing.