Richard Baker wrote:
If there is another Trek series I think they could do a lot more in making aliens have a non-human structure and still be dynamic characters which can deliver a good performance.
The Tholians (I think of "The Tholian Web") were a great example for a truly alien species, but presented here in a rather threatening context which equally applies for Babylon 5's
Shadows and others.
However, I think that part of the threatening appearance is the lack of discernable body language. Body language is important on an unconscious level and human actors under heavy makeup can still communicate in this "language" which is far more difficult or impossible for a truly alien being.