Mainly, Civilization VI is another Civilization game. If you've liked them in the past then chances are super high that you'll like this one. In the grand scheme of things it's not all that different.
But then again, the difference is in the details.
There are now more victory types and then can be achieved in new ways. Your city is no longer one tile but instead you build out districts and improvements that impact, expand, and limit one another depending on how you configure your city. Resources are handled differently. So are diplomatic options. Units can now stack in small quantities if you have the right research done, but there's no stack of doom like in old Civ games. There are a ton of small things that have changed.
Overall, I think this is the best starting place for a Civilization game that they've ever put out. It's inevitable that they'll come along with patches and expansions to improve the game. It should only get better from this point on. But even with the way it is right now it's a ton of fun.
If you've been a fan of Civilization in the past I highly suggest picking up Civ VI. If you've never picked up a Civilization game before but find yourself the least bit interested... I also suggest you pick it up. You might find a new series to love!