The Empire Strikes Back - Original Soundtrack

John Williams' follow up to the impressive Star Wars soundtrack is such an accomplished achievement and easily the best soundtrack from the series (which matches my feelings towards the films as well).  In three short years, he managed to make his original soundtrack sound like an amateur had composed it.  The Empire Strikes Back is a much more mature sound, much more confident and epic in its grandeur.  He has managed to take the themes from Star Wars and construct a more complex musical language to help tell the story.
The Imperial March would have to be as recognisable a piece from the Star Wars saga as the main theme is.  It immediately evokes feelings of dread and anticipation that something wicked this way comes.  But it's not simply a signature tune, it's BIG.  It's a Grand piece that embodies the majestic malevolence of Darth Vader.
Juxtaposed with this is Yoda's Theme.  A simply beautiful piece of music that is so melodic and yet so serene.  It can immediately reduce stress levels.  It is the music equivalent of Yoda.  Amongst the serenity, there is the heroic notes that tell us that not only can this 900+ year old wizard grant us peace, he is more than capable of single handedly rescuing us as well.   This piece is so sweetly handled.
Then there is The Asteroid Field.  A mix of Imperial March like music, the great lumbering Star Destroyers bearing down on our heroes as they attempt to escape.  Wonderful mixes string, brass and percussion.  The Love Theme between Han Solo and The Princess is a continuation of this theme while giving us the sweetness between our two lovers.
The Finale is a sweepingly brilliant theme that has a heavy thoughtfulness to it, leaving the audience to consider the price that our heroes have paid in their struggle against the Empire. Then, it drops back in to the familiar Star wars theme.  All will be well.
If you can only own one Star Wars soundtrack, make it The Empire Strikes Back, the best of an exceptional bunch.