Hernalt said:

Once the casting was assured with quality performers, he didn't really _have_ to direct them but rather let them loose inside the candy store of the set design, matte paintings, props, costumes, make-up, and play back monitors if they had them.

I take your point but I would say in return that there is a very noticeable difference between the performances the main actors achieved in SW77 and ESB. I think they all performed to a much higher standard in ESB and achieved much greater characterisations than in SW77. I would most definitely point to the change in director as one of the main factors causing that difference, another being a better script.

Also worth noting in SW77 is the difference between the quality of performance given by the likes of Alec Guinness and Peter Cushing as compared to the main actors - Guinness & Cushing are the sort of highly gifted and experienced actors who can give a polished performance no matter what. Case in point: compare the main actors' delivery of the dialogue with that of Guinness & Cushing - Harrison Ford famously said "you can write this shit but you can't say it" - Guinness & Cushing have no problems and the lines sound wonderful.

My point is that only the very best actors in the cast of SW77 could get past Luca$h's poor direction entirely. The main 3, Hamill, Fisher & Ford, could not and only gave the best they could give in ESB when given good direction.