Metallica have acknowledged the critical reaction to "Lulu", but think it will eventually be recognised as a classic album.
But it leaves them cautious over their future projects, including their forthcoming 3D film which enters production this year.
Speaking on "Lulu" (via Blabbermouth), Lars Ulrich said their collaborator found the criticism hardest to deal with.
"It was difficult for Lou Reed because he takes everything very personally. And I think he was very surprised. We told him all along: 'Listen, there are some very, very, very hardcore metal fans out there that like everything pre-packaged in a particular little box that looks like this, and the minute that you slightly veer outside of that, then they have a hernia."
He says the band needed to experiment with Lou Reed to "shake up" their career to survive creatively.
"The LA Weekly said how the real album of 2011 was 'Lulu', but nobody is gonna recognize it for another 20 years," said Ulrich. "In about 900 years from now, people will be able to talk about 'Lulu' face to face with each other without hiding behind masks."
Ulrich went on to talk about the Metallica 3D movie, which they seem to be approaching with caution after the commercial failure of "Lulu".
"Getting your own 3D movie off the ground is easier said than done, but we're doing our best," he said. "We just want to make sure that we don't throw ourselves out into something that gets so completely overwhelming that the whole thing just blows up in our face."
The film will follow a story of the band members against the backdrop of a Metallica concert, and will enter production this year.