Another one of these threads???
The original design from Alien didn't work with the story Ridley wanted to tell in Prometheus so he took SOMETHING FROM HIS OWN MOVIE, modified it, and made it slightly different to work in the new film. Yes, its a reton. Yes, we all know that. No, we do not all feel the same way about the topic as you do. And I'm sure that even the people who agree with you don't feel the need for another one of these complaint threads.
Personally, I like the Engineers as they are depicted in Prometheus, and it doesn't make me love the original Space Jockey from Alien any less.