I have some suggestions, such as:
- it could start with Fortress Age>Imperial Age>Industrial Age>Modern Age>Information Age
- Underwater combat: this would be a great concept for underwater battles with submarines, you can have a new view as underwater, I don’t see this concept in any other game
- Underwater combat is available once you reach Modern Age as you can start to produce submarines
- Air combat: it is introduced once you reach Modern Age
- Eliminate the concept of Capital City giving cards.
- Fortress Age: you have musketeers
- Imperial age you have slow cannons, and some units found in AoE3
- Industrial Age, you have the concept of machines and better cannons
- Modern Age: period of the world war 1 and world war two
- Modern age: you can start to build airplane fighters and submarine and unlocks underwater view.
- Modern Age: you can now build apartment buildings which give you 4x more population than houses.
- Information Age: you have a technology Global Position System, this one is very expensive, and it is available to be researched in the late game, it reveals map and has no fog, so you can see the whole map, similar to the cheat in AoE as reveal map and no fog
- Tanks are available in the Modern Age, but more powerful tanks, airplanes, submarines are available in the Information Age.
- Helicopters are available in the Information Age.
- You must upgrade musketeers from the Fortress into imperial musketeers in the imperial age, then, you must upgrade imperial musketeers into soldiers in the Modern age.
- You have now iron mines instead of stone mines, or both.
-Residential Apartments which give 4x more population capacity than houses, this will be the first time apartments and tall buildings would be insert in the franchise