T'other day on TCM, I caught a bit of Shatner's big-screen debut in The Brothers Karamazov with Yul Brynner, Joseph Cotten, and Lee J. Cobb. He played a very quiet, pious character, the youngest brother. In the parts I saw, he was mostly standing around in the background while the bigger stars were talking, or facing away from the camera while talking (or mostly listening) to Brynner.
I saw that in college back in the early eighties. I remember being amused that Shatner was playing the spiritual brother instead of the womanizing one--and that Hollywood actually gave The Brothers Karamazoz
a happy ending! (I was taking a course on Dostoevsky at the time and had just read the book.)
I taped it off TCM, too, but haven't had a chance to watch it yet.
(Are you sure Joseph Cotten is in it? I remember the three brothers being played by Brynner, Shatner, and Richard Basehart, with Basehart playing Ivan, the intellectual brother.)