A quick google image search for "dieselpunk" has proven there are MANY skilled artists out there who can do the retro.
I don't mean an EM machine from 1920-1950. I mean a modern game with dieselpunk style & flavor. Instead of regular looking speakers, have plastic off-white "vents" like on an old fashioned radio. Do away with the bright white & exposed wood, but moreso The World's Fair.
Make it look riveted together. Put vents where you don't need them. Think of the game "Bioshock". Big band music. Morse code. No start button, but a start "dial". Heck, throw in a Nixie tube somewhere.
The missions? Hmm, dunno. Beat the Baron. Assemble your diesel engine with 2 (locked) balls that go up & down in some enginey contraption. Drawings of babes like on the side of WW2 bombers for fun.
Ahh if I only had any art talent, time & money.