It's not at all like risk tbh
It's really one of those games that are relatively easy to pick up and understand but there's a lot of depth that you can get into with city placement (to tactically control resources for growth, as well as strategically powerful chokepoints for defense), tile upgrading, promotion perks for units (depending on where they are or what they are going to be attacking), build order for city buildings… It goes on and on, the skill ceiling is really incredible for where the skill floor is
If you can pick up both DLCs when you first start, that makes a big difference for how you learn. When I got Gods and Kings, Religion made a massive impact on tactics and even city placement, so I had to reteach myself a lot, but it wasn't tooooo awful cause a decent amount of the religion system was like 4's. I still haven't picked up Brave New World, but my brother has, and a lot of the changes he's telling me about just completely astound me because they're so different from what I'm used to, plus some of the new Civs added in DLCs completely revolve around new mechanics (Venice from BNW comes to mind; a very intriguing concept that's significantly removed from the standard playstyle, also Sweden in G&K which had a really cool playstyle which rewarded diplomacy and friendship with other Nations as well as City States over warfare [this was before the diplomacy revamp in BNW so they may have even changed again since the last time I used them])
Fuck Ghandi