I watch the eyes more than enough to be honest.
It depends on who's playing, maybe even if they play the game on fullscreen or not.
IT had moving eyes, and it worked great.
If the head movement didn't reach the eyes moved to the side so it looked like the character looked back. This was a small, but extremely nice touch. However, when you clicked on another character in IT, they head moved first, and as long as they were marked, it followed them around. Also a nice thing. Would look slightly funny if just the eyes followed and not the head itself