Sacrifice had the interesting conceit of using the souls of your defeated enemies as the "Vespene Gas" for making your new legions. In addition, it had you running around on the ground, not a deity figure like most RTS games have. The key idea was that you were a mage in the service of the gods because you're attempting to right a wrong you did and keep another mage from destroying this dimension. But that's not the point. Verticality is the point. And what if you could summon gigantic monsters? Think the Collosi, but bigger, and then have them roll face all over the stupid other forces or take on another giant monster. There could be physics on the monster, which should be made of something coarse like ground, so that it falls apart in real time onto the battle field and can totally kill people with it.
Furthermore, the game featured 5 gods of differing alignments and MOs, but it's presented too simply as "go pick mission from any of them". The game should read your performances- villagers killed, things summoned, types of things, and your strategy- so the gods coming to you is dynamic. Add in a bunch of different troop types, too, so you can spec power, defense, magic, etc., rather than just a common pool. You can even mix and match in a battle. Then, it could all just turn out that this was your character on a power play, getting in with the gods so he could get more power just for his own gain. The game should end with you getting the ability to summon and control any of the gods- as you summon them, show your character smile, then fade to black.
Sequel- the world has changed thanks to your leadership. You wield ultimate power and spend a few missions squashing anyone who comes in your way by battling with the gods themselves against puny mortals. Then, a change goes over the world and they start to actually power up and find ways to defeat the gods. You start to feel scared in your perch of power and have to appease the people or squash them. If you choose the latter, it ends with them summoning other gods and YOU HAVE TO HAVE A BATTLE BETWEEN THE DEITIES. Then when they destroy each other, you become a god yourself from all the power and souls laying around! If you go for the peace route, well, you don't get anything like that because you're not awesome. The game punishes you by being less good for going the responsible route. This one throws in a new thing to summon- a dark, extremely powerful one that corrupts you for an easy win. There will be some really difficult missions just to tempt you with it, but use it too much and you find yourself not a god, but an enemy of them, corrupted for use by another being. There'd even be moments where you don't control your character- whatever IT is, it's taken over you.