I think you missed out by skipping 5. With Vox Populi, it is the best current Civ experience in my opinion.
As for Civ 6...I have written so much about it already, I don't want to repeat myself too much. Suffice to say, I think it has a lot of good ideas, but a lot of lackluster implementations. I think districts are the biggest innovation over Civ 5, and I think they work very well in the early game...not so much in the late game. The mid to late game in general is a bit of a problem for Civ 6. It always is in 4X games, but Civ 6 is worse than most, due to the amount of micro management and busywork combined with a lack of automation and new things to focus on in the late game.
I'm definitely an "old timer" in this context by the way, as I have been playing since Civ 1. On the Amiga.