THE EMPIRE STRIKES BACK:
The best direction of the three.
The actors are more comfortable and confident in their roles.
More ambitious and polished SFX.
The introduction of new and interesting characters.
I would agree wholeheartedly with all these and add the following (all IMHO):
- the best soundtrack of the three films
- darker tone (less of a children’s film, making it even more appealing later in life)
- more atmospheric
Only suffers from being a middle chapter.
One could argue that being a middle chapter has its advantages, too. The film doesn’t need to devote too much time before “getting going” since the main characters are already known. And I often find the middle of a story the most satisfying: the plot twists and turns, leaving you wondering quite how matters will be resolved. The anticipation of the ending can be better than the actual ending. I’ve always loved the final scene of Empire: a time of loss, reprieve, and yet also of hope.