It's honestly my favorite 4X game of the last few years. I haven't tried any of the DLC, but the base game itself is really cool.
I think the thing I like about it most is that, unlike the last Civ game I played, what you research next is mostly down to RNG. At the end of each research phase in each category, you get a couple of choices that are basically random. So there is no clear path to victory or ability to quickly target an OP build, meaning the game is different every single time. There are still pre-requisites to different tech, obviously, and there are other ways to target them by searching out specific resources and such, but in general you can't just rush to dominance without a ton of luck.
Another interesting feature is the ability to discover primitive civilizations on a planet. You have the option of monitoring them from space, and maybe they eventually become advanced enough to start exploring on their own. Or you can go down and hand them the keys to space travel and see how it goes. Or you can just destroy them iirc, though it's been awhile since I played it tbh. Can make for some interesting scenarios, and politically the options all have ramifications at "home" based on your species / political system.
All in all it's a really well done game that moves away from other 4X enough to be different, but keeps enough of the concepts to be familiar and easy to pick up for anyone who has any experience in the genre.