To add some more why a lot of people like them, they've been around so long they originally pretty much crossed over with The Beatles and Rolling Stones, the Syd Barret version of the band was very much part of its time, a swinging 60's band with an artistic style, but still fairly conventional. Barely 5 years older than both bands so they still had a lot of that 60's London experience.
Over the years they changed so much that they were highly influential on the electronic ambient and techno scenes unlike most other bands from their era in the 60's. By 1978 Punk was writing them off as dead and done, as we've seen they survived and even picked some 80's and 90's style while keeping their integrity and packing out houses long after many of those punk bands died.
I think to really appreciate them you need to read up on Syd Barrett's descent and how they dealt with that, really is one hell of a story, some good autobiographies out there.
A lot of their appeal is the contrast between the highly accessible, soulful singing Dave Gilmour and the far less accessible Geddy Lee style mewlings of Roger Waters, who is not gifted with a soulful voice at all. Yet he still has a lot to say and his stuff could be considered be the more thought provoking 'harder listens' like the Wall.
Even some long time Pink Floyd fans like me aren't really that drawn to Roger Waters but still respect his output, but as has been mentioned the Dark Side of the Moon is both highly artistic and thought provoking along with a highly accessible musical style, pretty much why many regard it as their best album.
I've warmed a whole lot more to them these last few days thanks to this thread and this has only cemented that.
So especially dark side of the moon just has special weird memories for me.
