Wired.com writer Spencer Ackerman took some time to analyze the fictional Battle of Hoth from The Empire Strikes Back, and wonders why the Empire didn't completely crush the Rebels. Think about it: The Empire had nearly every advantage on Hoth, and yet the Rebels were able to escape with only the loss of Echo Base and some casualties. The core of the Rebel Alliance -Luke, Han, Leia- all survived and were able to plan the events that would take place in Return of the Jedi.
Be sure to check out Ackerman's analysis on the Battle of Hoth here, in which he dissects all of Darth Vader's decisions and explains why the Rebels were really the winners on Hoth. If you ever wanted to read an in depth break down on the Empire's space, ground, and invading strategies, look no further. Or is it farther? I never know.