After much thinking, it has to be The Who's Quadrophenia.

As a collection of songs it may not be my favorite, but as a whole, it really takes the cake. I appreciate a good concept album and/or rock opera, and this is probably the best one. It tells a compelling story, it has themes (musical and otherwise) that repeat throughout, it's really quite great, and, more importantly, enjoyable.

While I love Pink Floyd's The Wall, and others like it, some of the songs can be a bit of a slog when played on their own, which decreases the replay value of the album itself for me. Quadrophenia is the only double album where I actually love every song. They all work together to form the whole, but I enjoy them separately as well. I can listen to it all the way through over and over again without tiring of it. I just listened to it a couple times this morning actually.

It also helps that I saw the band perform the concert live a couple years back.

Anyway, if you haven't fallen in love with Quadrophenia yet, get on it.