What was it about the ship designs that made them so successful?

Difficult question. Both the Enterprise and the Klingon are uniquely designed ships that appeal to the mind because they look like they like they could work.

You look up in the night sky even now and you�ll see a 747 coming in for a landing and it looks just like a Klingon ship at night. It�s one of those just one of those marvellous things that that Matt Jefferies created. It just works. It looks good, it looks like it�ll fly, it looks like you could be there. Everything looks like it works.