Do note that I am biased against attempts at photorealism in games. I take this stance for two reasons. One, if you have the power to create anything, what a waste to simply use it to mimic reality. Sure, this is appropriate sometimes, but I'd rather it be a last consideration than a first one. Realism is not the be all end all of game "graphics". My second reason for being against realism has to do with a concept called "The Uncanny Valley". It should be MANDATORY that every animator and artist have intimate familiarity with this concept before being allowed to create anything. The gist of the Uncanny Valley as it relates to this discussion is, the more realistic a character is designed to look, the less convincing it is likely to be. The best visual design to aim for is a stylized character, whether we are talking about anime or DC comics or Saturday morning cartoon. For a better understanding of The Uncanny Valley, give it a Google. It's a valuable concept to grasp.
Okay, tangent aside, it's not the symmetry that bothers me in regards to the humans in Corruption, it's the (failed) attempt at realism. Well, and an unattractive design. Interestingly, Admiral Dane, who had a more comic book-like design, looked the best. Not that I particularly liked his design, but he didn't look as freakish as the regular crew.
Addressing Samus herself, I loved her head model in Prime, but I also took issue with it. It too was overly realistic. It looked good, but it didn't match the cartoon-clean, saturated color of her armor. Now, in Echoes we had the opposite problem. The armor gained a more "gritty" patina that the head model in Prime would have matched just fine. But in Echoes, Samus herself was cartoonified. She was very clean, texturally simplified, color saturated, and brightly lit. This created a rather ugly juxtaposition with the environment she was set in. Now, as much as I dislike her look in Corruption, she fit in with the environment she was in at the end of the game. However, I think the main reason may be the lighting. the light was very bright and saturated, giving everything a glow, so Samus's clean design didn't really stand out glaringly.