Hall definitely had "creepy" down pat. The women on the show seemed genuinely apprehensive around him, which helped increase the tension factor. As most others have said, though, I don't believe he would ever have been able to bring the nuances of the character that John Karlen did. When I watched these episodes in the early 90s (which was the first time I saw them), I felt that the tension factor actually decreased noticeably when Karlen replaced Hall. The fact that John was so familiar -- and I knew what was going to happen with him when Barnabas appeared -- the base effect was Willie Loomis changing from an authentic threat to an old friend having a bad day. In the end it worked out for the better, but I really did relish the tangible sense of menace that Hall conveyed. At that time, he was the one human character who outshone the supernatural in terms of sheer dread. Though his acting was merely adequate, in concert with the accomplished actors around him -- particularly Nancy and Alexandra -- his scenes stand out as being very dark and fear-invoking.
What he said. Don't even go there. I talked to John a couple weeks ago, praising the old man on his performance in the House of Despair CD. His protrayal of Willie is exceptional and when I gave congrats to JK, he said that, "I AM WILLIE".
As far as James Hall goes, spare me. He stunk. No one: but no one can hold a candle (blue or otherwise) to JK's Willie.