I find it very interesting how many folks (including myself) have a fairly wide variety of albums (and types of music) on their lists, yet U2's The Joshua Tree still shows up on so many of them (six lists in this thread, so far).
What is it about this particular album that seems to have attracted so many people so strongly?
It was an album that both defined the '80s and was yet counter to it.
Just kidding, I dunno why. It could be just that it's an album that had major crossover appeal.