Harrison Ford was never supposed to star in the film because he was too well known for what Lucas wanted to acheive. When he was helping out feeding lines to other actors who were auditioning, Lucas finally caved and realized that nobody else could play Han Solo. So yeah, REALLY lucky that Harrison didn't tell him to go stuff himself LOL.
George Lucas is definitely not an actor's director. He has no concept of how to pull out from somebody what he's trying to convey. Mark Hamill's acting improved greatly in Empire with Kershner at the helm. Same with Carrie Fisher.
I'm watching Episode IV right now! Wheeee!