I think you could have done alot more with coming up with an actual concept instead of a basic straight forward paintover. The technical ability is getting there. However, there are a few areas that show lack of skill in perspective and rendering. Work on perspective!
For an image. I actually like it. But with such an awesome form as what you have here. You could potentially make something breathtaking!
I know, this right corner down there looks sh*ty. There's actually a big gun there but i somehow painted over it and now it looks like false persp. But the rest is actually fine.
And concerning design: yeah, i could probably push it more. I lost those spikes somehow, yes. Will maybe think about it.
The image looks okay at a glance, but you need more than a decent palette and sketch lines. The airbrush or dodge tool has been over-used, since that's what I see instead of your drawing. The more of a story you can tell about this machinery, the better. Good designs convey a sense of function and potential, and this is still just a big wheel with lights on it. Technique isn't too bad though. The texture on the wheel is a little overdone, but it's not bad.
since everything that needs to be said has been, what i want to talk about is using refs. please do not get a picute and draw directly over the image. it shows a lack of creativity. what refs are really god for its getting an overall feel to a piece. in this case like an industrial feel. get many industrial feeling images, and use them to make your image feel the image way. look at the ref and determine why it gives off a certaint feel. like why dose the wheel thing like like some industrial piece of equipment. get that into your piece. you can use bits and parts, but dont just paint over. its fine for practice, but leave it at that.
I like doing the same thing- But instead of painting over it and making something literally out of IT, try making something it Inspired. Say you made a bike with this HUGE wheel. Or some sort of vehicle with a huge front weel. Y'know.
EDIT: Also, something I might be wrong about; more contrast. It's a very dark piece, and there isn't much obvious gemoetry aiding the composition... Good luck!