One of the creepier CG sins is to make skin look like plastic. This was only one of many many things wrong with the Scorpion King character above, who actually only appeared in scorpion king form in The Mummy Returns and not in any of the three movies actually named The Scorpion King, because Hollywood likes to confuse us. (Yes, it had two direct-to-DVD sequels. No, nobody watched them.)
When moviegoers say skin "looks like plastic," it can mean a few things. Sometimes they mean faces are rigid and motionless, as if they were made of hard plastic like some kind of creepy doll, which is usually a rigging problem, which I'll talk about later. Sometimes they mean the skin has the texture of plastic, like their face has been shellacked.
Sure, this was 11 years ago, but let us note that the Rock lent his face to this hilariously shameful visual effect the same year that the first Lord of the Rings movie came out.
They hadn't reached their full potential yet (Gollum comes along in the later movies), but clearly, plastic-Rock-head-pasted-on-monster was not "the best you could expect from CG at the time" by any means.