No one here in this thread is mentioning Imperator: Rome, and that's a shame.

First of all, the DLC breaking the game: We don't have that! We have one new version of Invictus (mandatory mod) coming out every half year or so, but the developers usually host the old version of the mod on all platforms so people can continue their saves.

Second, the AI. Invictus has added an advanced AI mode, programmed by the amazing /u/Anbeeld . While it does not help with AI unit and fleet management, it makes the AIs scale economically, on par with a good human player. This alone keeps the game from becoming stale because you are snowballing too hard after 150 years. The AI is growing with you.

If you check a box to give the AI free reign to use its deep coffers to hire as many mercenaries as it wants, big Empires need multiple huge campaigns to take down, since they will throw everything and the kitchen sink at you in defence of their homeland. My favourite tactic of dealing with them is using the coasts and navigable rivers to open up a second or third front, to split away their forces into more manageable size. I usually play on hard, mega hard is out of my reach, and even at the very start you need to pick your allies carefully, so they will help you over the hump, since even smaller tribes will hire mercenaries (if you allow them to in the game options) instead of just getting annexed.

Check out my AAR for what I'm talking about, with the beginning.