Here's my take:
* Visual Influences - Best example off the top of my head of the range of visual influences I'd draw on would be with the origin...
- Krypton: A futurized amalgam of Ancient Rome and Egypt, Medieval England, and Feudal Japan; essentially, the lost civilization of tomorrow.
- Smallville: A mix of S:TAS and "Superman For All Seasons", with elements of my own hometown thrown in - JUST out of touch with the present day, sort of in the opposite direction of what I'd do with...
- Metropolis: A combo of the most decadent and high-tech aspects of New York City, Tokyo, and Dubai, with slight traces of Robocop's Detroit, Rick Deckard's L.A., and Marty McFly Jr.'s Hill Valley - basically a comparatively ancient 'base' version of what Kryptonian civilization ultimately became.
In terms of production, Krypton would probably have to be shot entirely green-screen with small sets and CGIed later; Smallville would be locations and sets; and Metropolis a mix of all three.
* Atmosphere/Tone - Somewhere between "Raiders Of The Lost Ark" and "Back To The Future" - dynamic action sequences, modest-to-brisk pacing, and a generally upbeat tone with a few tense moments.
* Colors - All over the place. The movie would be sort of the opposite of Nolan's Bat-films in many regards - kind of a modern-day version of "The Adventures Of Robin Hood" - particularly in terms of the basic pallette of the film.
* Language/Dialogue - Very formal and pronounced on Krypton (which, BTW, would be subtitled, in reference to the early SW and ST films); very down-to-earth and less formal in Smallville; and very snappy and Hawksian when we get to Metropolis.
* Era/Time Frame - Not really determinable, a la S:TAS; there'd be elements that would be retro and elements that would be futuristic, but nothing that really roots in either one, and not in the present...basically it exists in its own world.
* Costumes - Kryptonian costumes would carry the same historical influences as I mentioned above for Krypton - lots of serpentine jewelry, multicolored togas and tunics, headdresses, armored motifs like epaulettes and shinguards, etc.; outfits in Smallville would be the more practical outfits you'd expect to see in a small farm town - lots of coveralls and flannel shirts and sweaters and sneakers and blue jeans and Sunday best and the like; and wardrobe in Metropolis would have a wider, more fashionable range.
* Music - Not much of what passes today for 'pop music', that's for sure. Musically, the only things at this point I know I'd do are with the score, and that's 1) to make the sure the main theme music carries the same three-note motif that has been a part of the radio show and Fleischer cartoon theme, the George Reeves TV show theme, the Christopher Reeve movie theme, and the S:TAS theme, and 2) to make sure there's a leitmotif structure for every major character - each of the major villains should have their own theme music, etc.