I played through a game on normal in Imperator Rome as Rome.
I'm basically just scratching the surface of a game like this, but it feels like a game where you're trying to find the dominant strategy, and not necessarily a mechanically deep game. The most interesting mechanic I found was intentionally failing to enforce peace. It would make you enter a war, but you didn't need to worry about CB's or stability. It's free real estate.
The Roman Republic (precursor to the Roman Empire) fell apart for a few reasons, so if you never allow your generals to get too powerful and disloyal, and aren't shy about replacing them, then that's a major threat basically gone. Another significant patch or two and this could be balanced.
Diplomacy needs a huge overhaul. I didn't really ally or feel the need to cooperate with anyone until late in the game when I wanted to ally with Egypt (as a check against Carthage and the large empires in the east I was running up to) but couldn't do it because I was too big of a blob. Alliances can be exploited (see the HRE in CK2), but it made me disengage with diplomacy in a game where you play as a nation.
In these games you generally want to go wide, and keep expanding rather than build tall with lots of improvements in each province. There is a 'macro builder' button where you can plop all the buildings you want, so it encourages a formula of building the necessary things, and then just leaving it.
There's also shockingly few unique events, even as Rome. Giving the game like this a bit of optional structure isn't bad. The available missions don't really provide you with flavor text usually either, so it lacks world building.
It's not really a bad game, but it is sort of a letdown compared to CK2 and EU4. Paradox has a build your own bundle with Humble going on right now, btw. I'll note though that CK Complete is CK1.
Paradox Build Your Own Bundle | Humble Store