Though I struggle to understand what everyone finds so great about ESB (not even close to being my favorite), I will give them credit for the fact that it’s the one SW movie for which I can’t think of anything to improve upon. That probably stems from not knowing what exactly it’s lacking.
Out of curiosity, what is your ranking from favourite to least? Having a sense of what you value in a Star Wars film might help illuminate what you feel is lacking in ESB.