Subjective question has subjective answer...

This highly depends on what other games you play are.

If you like Civilization, particularly older versions like 3 or 4...      One or two games?

if you've never really played a lot of turn based 4x games...      much longer.

There's a learning curve to be sure.  Stardock has continually tried to make the on-ramping process easier throughout the series, but at the end of the day it's simply a complicated game.

At heart it's a tinkerer's game.  Lots of fiddling around with stuff, trying things different ways - succeeding some of the time and failing some of the time. 

It's a great game and I've always felt like I learned something new, or exploited a unique situation in an intuitive way, pretty much every game I play.  Much of the design is very much to present different situational challenges every game without a straightforward solution (much like running an empire would be), which can be confused as not understanding the game well enough.

Hope this helps & welcome!!

-tid242

IMO two is a tougher sell the younger generation. I’m 32 but I game with mostly people in their 20s if it don’t look pretty they ain’t interested of course players interested X4 seem to care a little less about graphics and more about gameplay. However the art style in civilization 6 was so off putting I haven’t completed a game meanwhile I 2000 hours in Civ 5.

Also galactic civilizations 2 is a damn excellent game and why I brought 3 when it first released.

also play on lower difficulty and as you figure out what’s going on ramp it up even on normal these games AI will come at you hard if it sense weakness and they are warlike. 

As has already been said this is a subjective questions with a subjective answer. And some games just aren't for some people. The best way to answer for yourself is to compare to any other turn based and 4X games you've played.

I played all 3 and I'll liked GalCiv 3, but I'll echo Divine Wrath. GC2 is more straight forward.

Fingers crossed GalCiv4 will be even better.