True, I remember the first time I saw Gollum in Two Towers. I was freaked out like hell, he was just so different from everything I've seen before. And Andy Serkis played him so well. Not to mention the CGI was just off the charts. So if it freaked me out, I can only guess how Tolkien would react, given how much of a leap this would be for him.
I think he would flinch a bit, ride out the rest of the film on the edge of his seat and I hope that The Professor would nod and say "Well done, good actor, and well done you cinematic makers of marvels" or something to that effect.