The original Star Wars movies were great because they had great characters. That's what Abrams needs to get right. The dark themes in The Empire Strikes Back were so compelling because people cared about the characters. When Lucas tried to recreate those darker moments in Revenge of the Sith it was laughable because the characters were so poorly constructed.
I agree with you about the nice contrast that exists between A New Hope and The Empire Strikes Back. I'm not sure if the wonderment from a New Hope can be equalled at this stage in the franchise, or in this stage of movie history for that matter.