That's pretty awesome, I must say. The placement of the gun is pretty hilarious, but I think it looks good in its own way. As for the physical design of the Feminine body and the Spider Machinery I say good show! I especially love how the enlarged brain (to coincide with the Spider Mastermind-esque Appearance) gives an illusion of hair, though I wish that'd been played up just a little more. The way the machinery is setup was very well conceived, I am loving how the circle forms around where the flesh legs meet the body and how clearly developed the jointing in the legs is. You also managed to succeed in giving an ooey-gooey look to the undercarriage at the baby releasing mechanized pseudo-penises so I have to say I'm impressed by that.
I really think this would've been a greater design for a Mini-Boss intended Monster than the base Vagary we received, I could especially picture this thing rearing up and launching arachnotrons at the player like living missiles... Just such an awesome image there.
I've had similar experiences with art competitions, though almost always lost out due to my work being black and white and over fifty percent of everyone else's having color. As for the underworking of Doom 3 Elements, it's fine, but for where the female body meets the mechanical/Arachnotron-esque (I.E. The brain, the gun, and the connecting wires) just a smidgeon more attention would've gone a long way, while playing up the brain hair look would remove the "stout neck and small head" feeling she gives off at first glance. Just stuff to consider to help you think through future designs.
I also totally get the over fan-loving of Classic Doom. While I still do and always will love Classic Doom I do enjoy quite a bit from the new designs and love to mix-match aspects of each. Hope to see more intriguing work from you soon, especially if Doom related.