An RTS that can have as much or as little micromanagement as you want, and for both to be viable strategies.
For example, you could anything from entire armies to just one guy, even where that one guy shoots, and everything in between.
I don't care what setting it is, but it'd be cool if you could set what it is when you start a new singleplayer game, you choose what era, maybe a medieval one, a modern one and a futuristic 'IN SPAAAACE" one. It'd be super special awesome if instead of eras you chose what year it takes place in. Of course, if you start in the medieval era you could go all the way to the futuristic era, completely seamlessly. Bonus points if you're blasting off and colonizing planets when everyone else is still discovering steel.
For super awesome mega ultra bonus points, there could be a preset human race, and a player set number of procedurally generated armies each with their own strengths and weaknesses.
This would be the best game ever, in my opinion.
The singleplayer campaign would not be unlike Medieval 2: Total War in how it's played, but instead of inciting battles with other pieces, you can just scroll down to your army and see them marching closer to the enemy. While being completely seamless.
Don't care much for graphics, but I would prefer it not to be in ASCII. Something like Medieval: Total War (the first game) would be perfect.
Now if humanity could just invent a computer to run it...