Actually, quite the opposite, for a species which resorts to personal and collective aggression first, and reasons later. ProfessorTrek 00:00, August 7, 2011 (UTC)
I think a lot of that has to do with cold-war thinking. When the originals were being made, everybody had to feafr the mysterious russians or be branded as a witch-er-communist. Accordingly the klingons were made to be standoffish, violent villains. Undiscovered country is a fine example of this-nothing about honor, mythology, or any redeeming features at all. They were just there as a force on the other side. This is, in my opinion, one of the reasons why the later series are so much better-the enemies come in different forms. The Ferengi and Klingons are really not evil once you understand their culture (however frightening said cultures may be to us, especially ferengi misogyny), so it's harder and harder to use a typical klingon or typical ferengi as a villain-exceptions abound of course, but the typical klingon has a lot of depth to him/her now, and even when seen as a villain, it's usualy with respect and understanding.
That said, there're still plenty of evils. Cardassians and Romulans make for much darker and mysterious villains, respectively, than any TOS klingon. The borg and dominion seem rather cliched sci-fi villainous types, but I love them both and they make for great TV, and, as in FC, a great movie.