Interested to know... Is it that you didn't like the movie so the "big humans" stand out like sore thumbs and make it worse for you or that regardless of what else might have been improved for you (be it script, the 'science' etc.) "big humans" would have just ruined it anyways?
The single biggest problem I have with the film is composed of two, interrelated elements.
It was the "Von Daniken/Ancient Astronaut" angle, and it's directly related consequence of retconning the originally alien Space Jockey into big Humans in suits.
While I admittedly had a lot of other problems with the film, the aforementioned is my biggest complaint, and which effectively "ruined" the film, for me.
And again, I have absolutely no problem with the equation: the Space Jockeys = The Engineers.
In fact, I kind of thought this was a given.
The equation I do have a problem with is: The Space Jockeys/Engineers = Humans
Thanks D - well I'm not a lover of the 'small universe' factor... and engineers creating humans does make the Alien universe a tad smaller. However I do like the angle of humans being a failed/aborted experiment and the notion of our biggest enemy/danger being those that created us. Not sure how they'd have made that angle gel better - perhaps have left it for a twist at the end of the movie rather than the 'they are us' reveal early on?
I personally would have also cut the opening scenes with the engineer sacrifice (as nicely shot as it was), as again this took away from some of the mystery and made their culture seem a little more 'human-esque'.