Love it. =)

Great job.

Looks really nice.  I like it :)

I agree with Redshrike about the pipes in the background, they do stand out a bit. I think the main issue here is that while the rest of the background gets darker as you move up, the pipes stay the same. I think if you keep the brightness of the pipes at the bottom and then gradually make them darker moving upwards at the same rate as the rest of the background they would blend in a lot more.

Hmm... I'm not too sure about the pipes.  A little bit of that banding effect can be good, but with it in those quantities it almost looks grooved, and the overall brightness of the pipe distracts focus from the character.  I'd suggest that you remove most of the 'banding' effect, and that you also tone down the brightness a bit.  Adding a bit of texture might be cool too, perhaps some wear and tear or corrosion, maybe some red or green hues.  The pipes in the bg also seem a bit bright; they might also benefit from just a bit of toning down.