I enjoyed doing the gag covers better than the story ones because they were usually simpler. A cover based on an incident in the plot took a great deal of staging to tell a little story that was still part of the book. And it had to make sense on its own.
I would have to say I'm bored with the standard rock, guitar solos, but I've done it for five albums now, and this time I wanted to go in a completely different direction. I wasn't interested in showing off any more.