The first part, Buckaroo Blues, is about cowboy music. It's one of my favorite Residents works, just because of "Bury Me Not" and "Cowboy Waltz". I haven't heard the original versions of these songs yet, but I highly doubt I'll like them better.
Black Barry, the second part of the show, concentrates on "slave music". I'm not really familiar with that kind of music, but I like what The Residents did. It's got loads of sampling all the way through, and I sure love to hear sampled music. So it's basically what makes this part of the show so great for me. "What am I Gonna Do" is the best song in this part of the show.
The last part, The Baby King, is all about good ol' Elvis. The Residents have released a full-length album called The King & Eye, and it's FAR from being one of my favorite Residents releases. When performed in the show, the music doesn't really get any better, so it's the weakest part of the show for me. However, the first song, "Ober", is indeed one of the most epic songs I have heard. "Love Me Tender" is kinda nice to hear too, and the ending is surprisingly effective.
However, the music is only around 25% of the experience. The visual performance is what the show is really famous for, especially in Buckaroo Blues, with the dancers in blacklight suits and cowboy hats around a glowing campfire. The Residents really put a lot more effort into the costumes and coreography than the music. That may hurt the experience a bit, but I really don't care much. This is still an amazing project, and an important part of The Residents' history.