Rev. Syung Myung Me: This was, according to lore, the second Residents album recorded, although it's tough to say whether or not that's actually the case. The story is that The Residents recorded it, intending it to be only released when they had forgotten about it, allowing them to operate under the Theory Of Obscurity, which says that the only pure art is that which is made with no considerations for the audience in mind. Since they never intended to release it (at least releasing it while they remembered what was on it, anyway), they could record it for themselves.
People who argue that the story is true point out that on the back of The Third Reich N Roll, Not Available is teased. People who say that The Residents made it up to have a cool story around the record point out that it's a bit more polished and the equipment sounds better than that which they made Meet the Residents and the first half of The Third Reich N Roll with (as that album was recorded in two separate sessions a year apart). I think the general consensus is that they either started Not Available when they said they did and finished it around the time of the second The Third Reich N Roll sessions, or recorded it all around that time. (Some people even argue that the mention of the missing Not Available second album on The Third Reich N Roll's sleeve was a joke that they later recorded the album anyway. I don't think that this instance is true, though.)
As for the album itself – it's often listed as Residents-fans' favorite album, but I've never been able to get into it. It's all right, though, but not someplace I'd really recommend starting. But everyone else likes it, so maybe it is a good place to start. But I probably wouldn't have been as into The Residents if this were my first. The album is intended to be an opera, although the story doesn't really seem to make a whole lot of sense (not that that's a bad thing).