I love designing Album Covers. They're some of the most fun projects a designer can have. Because of the creative nature of those involved (ie: musicians) and the history of design in the music world, clients are generally looking for something very creative and original.
Naturally, the design direction for any project, starting with the album cover, is informed by many things, such as the client's budget, the musical content of the album [and what it inspires] and the clients taste.
Generally clients will have some suggestions or requirements (such as including particular artwork that they did themselves and so forth) that will often set the tone of the design project.