If I ever get a chance to work on "Age of Atlantis", I'll emphasize that this game world will have an archaic flavor to it. Aside from there still being dinosaurs and the like around, the architecture of even the major cities will be based on ancient designs, such as Classical ones and those of the Aztecs, Mayas, Incas, Egyptians, etc. Military gear, particularly armor, will look as it did up to the time of the fall of Rome, with helmets having crests, or at least a spot to put a crest; even full plate armor---or powered armor, if I allow it in the modern stuff---will look like Greek hoplite armor or a Roman legionary's outfit. Maybe instead of automobiles, aircars, etc., modern land vehicles would be chariots pulled by robot horses. Imagine an enclosed chariot like this, with air conditioning, a radio, and all the trimmings of today's latest cars; sounds like a nifty piece of "treasure", doesn't it? Even the psionic powers would be described in such a way as to resemble magic. Perhaps mental images could be formed in the air when you use a psionic power. For example, if you use pyrokinesis to set something on fire, perhaps an aura or image of flame or a fireball could appear in midair and connect with the target before it burns up. Or a flying or levitation power creates an energy aura around you that includes etherial wings.
I didn't have time to finish my talk on "Coup of '45". All the fighting and intrigue would take place in the US. Remember that the main conflict is a civil war, with plenty of opportunities to get opposing units to defect. Also, when Mexico invades, the California-based units of the two US combatants will unite to defend Los Angeles, and when Japan eventually invades, the Mexicans will form the same rogues' alliance with them to keep the "non-North American" people out.
Truman's side holds the northern US eventually, but has trouble getting enough recruits for the ground forces; everyone wants to fly a plane. However, he has maintained control of the old US Government's POW camps with hundreds of thousands of German and Italian prisoners of war, and is eventually desperate enough to hire them as mercenaries. Remember how much of Germany's ground weapons---tanks, antitank guns, machine guns, etc.---were superior to those of the US? The Truman government was making plans to produce some of those arms, copied from captured arms, on at least a small scale, so now they do so in Pennsylvania, effectively making the defense of that state the responsibility of the hired German and Italian troops. So yes, you can be part of the "Pennsylvania Panzers" in this war, fighting for Truman until the time comes to betray him (at the moment Germany invades the US with its reconstituted army well-equipped with wonder weapons).
The German and (to a lessor extent) Japanese secret weapons will be the big draw in this came for novelty seekers who miss magic and psionics. Who could resist playing, say, an Me-262 jet fighter pilot in a world of propellor-driven planes? Or the commander of a Tiger tank---or a company of them---when the opposition is driving Shermans, and for once your side has enough air cover to watch your backs?
I'm already thinking of doing a novel on this subject, game or no game, so I've already done a lot of research on it. There are lots of sources on Germany's secret weapons, with the definitive one on her aircraft projects being the book "Last Talons of the Eagle" (don't remember the author at the moment). For futuristic German tanks, try Achtung Panzer's website (www.achtungpanzer.com
) for vehicles like the Panther II and the Lowe (Lion). Also study the King Tiger section; there's a paragraph in it concerning the proposed "Klein Tiger" or "Small Tiger": a Sherman-sized vehicle with sloped armor and a potent 100mm gun. For Japanese aircraft developments beyond late-war models like the Shiden, Raiden, Reppu, Frank, and Tony, try---as I did---the Hikoki 1946 site (http://j-aircraft.org/xplanes/
). It's a treasure trove of unheard-of models of fighters, bombers, etc., both prop-driven and jets.