McQueen had a bit part in "Somebody Up There Likes Me". I've seen it, and I would not consider it to be outstanding. I think the original question was "greatest" film debut of all time.

I'm in agreement that Peter O'Toole in "Lawrence of Arabia" would qualify.   The other films mentioned were good, but that was a classic.

As for Kathleen Turner, it was a hot debut - but can you name another decent film that she was in, or what her last film was?