Honestly, the harder they try, the less imposing the villain'll be.

I find Sauron in the 1978 version to be far more imposing than Sauron in the Peter Jackson version, and you know why?

I find Sauron's design over-the-top trying to be scary. What with the spikes all over his uniform, and the over-the-top death.

In the 1978 film, however, he's never seen, and carries more of a presence because of it.

That's why I think the Emperor works. Two films of buildup, and his design isn't too over-the-top (even if his voice is), but he's still imposing when he shocks Luke with lightning from his fingertips.