@boomerang,
Hi Boomerang - I was going to start off with 'great sound, great songs, great musicians' and then waffle on mindlessly - but I thought I'd do some research and I'm now very glad you asked the question because I learnt a lot from the Wikipedia entry on the album:
http://en.wikipedia.org/wiki/801_(band)
It was the first live album to use DI!!!
I think the other great thing about it was that I hadn't had much, or any, exposure to the studio versions of the tracks, and where I had the live versions were brilliant adaptations/innovations. As an example Brian Eno's original 'Baby's on Fire' is a slow paced menacing number whereas 801's is a rollocking ball blaster that you'd be happy to drive off a cliff to. I just love Bill McCormick's tasteful bass-playing in RongWrong merging into more frenetic quasi-funkentwhistle playing in Sombre Reptiles.
Even having the crowd flange into the intro of Diamondhead is live studio trickery.
Reading the pedigrees of the members (courtesy of that wikipedia link) is amazing. Some of the players were the products of cross-cultural unions, Eno was from another planet, and most had very distinguished musical CVs pre and post 801.
I even found free illegal download of the album (my vinyl can stay in its pristine cover!)
http://zambonisoundtracks.blogspot.com/2008/11/801-801-live-1976.html