Overall it's quite fun and it will eat all of your time. It definitely has that 'civilization' vibe where you look at the clock and it's suddenly 4 hours later than you had expected!
I think with DLC and modding this game will have extremely long legs. Right now diplomacy/espionage/etc will need to be fleshed out, but the game has a lot going for it.
Aside from all the usual 4x stuff what is really fun is the writing. The game has a lot of personality, and there are tons of optional 'quests' for investigation or plot that you can explore. Tomb worlds, fallen empires, etc.
Fallen empires are a great concept, think of an ancient isolationist race that wants nothing to do with you unless you cross 'x' boundary in territory or research a dangerous technology, then they come out swinging at you with end-game tech to punish.
Another super-fun thing is the ability to observe and 'uplift' other primitive civilizations. XCOM in reverse where you are the aliens. Observe the primitives with non interference? Genetically modify your own species to infiltrate their leadership and prepare the planet for annexation? Gift them your technology and uplift them to the stars, and they will be forever grateful?
Here's a cool screenshot form an 'alien' playthrough coming across a 'primitive' earth
I haven't gotten into multiplayer yet but apparently you can jump in/jump out and it's a lot of fun.