Nigel Terry gave an exceptional performance as Arthur. He did a convincing job of growing from callow teenage squire to kingship and maturity. I actually admire his performance more than Williamson's as Merlin, which was a little over-the-top for me. Of course if you've got Williamson you have got to expect over-the-top. I see what he was going for, his Merlin is not entirely sane, not entirely human, but he didn't entirely convince me. I did enjoy his scenes with Mirren, though.