Ok the Legs look poor, but there are limits... but this could have been done better with more time and budget, and i am sure they did for one Monster use like Bladerunner (Running Prosthetics)

So indeed i think they could have done a few shots like this... but then done some more closer Practical Effects Shots..
Remember the Alien Suit for ALIEN was a bit shabby but was ahead of its time, it worked by limiting how much you saw it full on...
The Neomorph suit looks a bit iffy.. but again CGI overlay could have Polished it up...
The Full CGI version, especially the Adult just looked Poor the Mouth looked awful... yet the concept it looked great and no doubt a Animatronic Practical Effect would have looked great.
Its shame that as with Prometheus it appeared Props was worked on but not used (some of the Fifield Concepts built).
Looking at these Behind Scenes (Thanks to AVPGalaxy) it reminds me so much of what could have been.. and brings me to this Video.
The Thing Practical vs CGI
Another Clip of Practical stuff