I was definitely grossed out when I saw that creature on the IMAX screen for the first time. Could not have been any more apparent what they were going for, which I think added a lot to the scene. Although I do think it was disappointing how it killed the engineer.
It could have been scarier to extend the chase with Shaw, and perhaps the Alien could have come out of the engineer, and Shaw is back in the pyramid. Then again, maybe that would have been tiring and too similar to the original.