I loved IV and still hold it up as the best Civ game. Unfortunately I no longer have access to it, and so can't play it. I find that VI does improve a lot on V, but ultimately I felt that V was a massive step down in almost every way (though I like what they've done with combat no longer being a single random dice-roll... but even then, IV had much more interesting promotion trees)...

Anyway, that said. Civ VI is still pretty competently made, with the exception of some incredibly severe imbalances with the civs themselves.