It's not really cel shaded, and the subject matter isn't really steampunk. Technique-wise, it's really just a sort of digital reproduction of the look of a pencil/marker concept rendering. Stylewise, it owes a lot to Joe Johnston and a little to Enki Bilal.
It is absolutely marvelous the way it looks! I thought may be there is a technical term for it. But the description you gave is good enough form to do more search and find out more about the style! Thanks mate, very nice work!
Thank you, I'm glad it's proved useful. If there's a technical term for it, I'm afraid I don't know it. More than anything, it's a reflection of a certain set of tools and techniques to do concept and design renderings back in the 1980s when everybody still used those smelly markers. It's what I grew up with, you see.