It's worse than you can possibly imagine. 2 words sum it up very nicely... Wookiee Porn.
Bad makeup, questionable sets, Bea Arthur and Harvey Korman singing, Carrie Fisher obviously very high on something or another.
It is noteworthy because of the unused ANH Vader footage, the involvement of the whole ANH cast, Ralph McQuarrie designs, and a few others. To quote a teacher of mine the producers "snatched defeat from the jaws of success"
I have it on DVD and have watched it several times. I highly recommend the Rifftrax commentary.