“The Force Awakens” has an energy to it that perfectly matches the tone of the film. Might be in contention for my favorite subtitle. “Shadow of the Empire” sounds like a boring EU novel (in other words, does not match the spirit of the film, even if it does relate well to the content).
I think in general, throwing “of the” gives the title a passive sound. For Star Wars you want the title to be exciting getting you invested in the story right from the start.
For example:
Attack of the Clones VS The Clones Attack
There is something about the latter that sounds more exciting. It’s not the best wording but it feels much more emotional than the boring former. Although I suppose AOTC did it’s job as a title- it was indeed a boring movie!
The Force Awakens VS Awakening of the Force
The latter makes me think of a slow film dedicated towards exploring the force, while TFA feels like a modern blockbuster. In which case TFA did a good job choosing titles.
Return of the Jedi VS The Jedi Return
Here is a special case where I prefer the passive variation. The latter is a too much over the top. ROTJ is very elegant, matching the epic nature of Luke’s journey in this film.