The game world is divided in several islands, each with stonger enemies. After a well paced first island that acts as tutorial and a decently paced half of the 2nd island you run into a stone wall of attrition where enemy armies are impossible to defeat unless you fight, sacrifice your entire army, go build a new army and fight the now reduced numbers of the enemy in a second or even third battle. There is option to retreat but if you do without losing the fight, you lose your army without inflicting enough damage for the 2nd round to be easier, so you need to relly on RNG that you will fight to the last man and survive to come back. And that gets worse as the enemies get stronger.
I backed this game on kickstarted and i was very satisfied with the result. They even implemented a couple of points of feedback i gave them. My only real issue with it is that they make many promisses and kept them, but to keep them they compromised some of the depth they could have added to each. For example, as backer goals were reached, they added new levels to the mega dungeon but to manage to make all the floors, they had to make most of them really small.
I will agree with the rest of the positive reviews here that the historical campaigns are really well made. However the real essense of the game is the skirmish mode where you can get your faction from the stone age to the space age and have to fight the others for resources and territory as you make your town bigger and advance from age to age... And this is where the problems start as the game cheats really hard! On normal to be able to keep up with the AI, you have to use half of your population or more for resource gathering, while the AI always has more resources than you, always sents troops to attack you and always is one age ahead of you, and all that without having a single worker gathering resources. That was the reason i lost interest in this game and never gave a chance to any of the other games in the series.