Millennia

The obvious comparison here is gonna be to Civilization, and that's a tough match-up. Paradox however would be well-equipped for the challenge, but Millennia doesn't completely live up in my opinion. It's worth a play, the things it does different bring a fresh enough spin to the formula to be interesting and engaging, but that's about where it ends.
A lot of systems are barely explained, with the in-game encyclopedia having practically no information, leaving the whole game feeling fairly incohesive. The concept of ages is neat in theory, but due to the nature of being a turn-based 4X it can be very frustrating heading down to an age with no way to change it besides waiting for another nation to initiate the transition; you can be notified of not catering to your population's religious needs with six turns remaining until you're locked into the age of intolerance. Fine and dandy, until you realize the only cities you can build religious buildings in will all take more than six turns to complete and you're left sitting on your ass while the game yells at you every so often.

It simply feels 'not quite there', which is an overwhelming experience in this game. Having different XP's and powers for things like diplomacy, warfare, etc. is an interesting concept but in practice it just leads to a lot of 'I have no idea how to increase my arts XP' or tabbing through all the power menus trying to find what category the 'build town' power is under. The game has a few preset civilizations, but all that entails are the visuals of your nation as the nation perk can be selected independently. On the other hand, you can build your own nation, but that only includes a general namelist and building set, leaving you with the most mediocre of both worlds; making your own nation is not expansive enough as you can only use the already existing names (like having Aztec city names only), leaving you unable to truly create a custom, interesting nation, and the preset civilizations are not unique enough to feel like you're truly establishing, say, a Roman empire. This is especially disappointing as another Paradox title (that even uses namelists!) where you can create your own empire, Stellaris, absolutely excels in allowing you to make something truly unique.

The missed potentials even seeps through into the more minor gameplay details, like there not really being any useful overlays, or not having eligible targets highlighted when using a power like the 'expand town' one leaving you manually hovering over each of your towns to find one you can use it on. That particular problem isn't helped either by the weirdly obfuscated melting pot of development systems where you have towns, town levels, outposts, regions, region capitals, region levels, and vassals, all of which are barely distinguishable from one another. Multiple times i've attempted to upgrade a city in my territory only to find out it was a vassal all along!

All in all, this game does enough in concept that I feel that, long down the line, given enough expansions (and knowing Paradox, that will be the case) and mods (same story), this game can be a truely worthy alternative to Civ. Currently however, it's just a temporary change of pace and nothing more.