Civ 2 is better, it's got a bit less detail (i.e. less endless managing of cities...), and got the more aged graphics to boot. Then again, it's already got the the isometric perspective.
The one big improvement of Civ 6 I can attest to is not having to build individual boats/ships for melee units once you have the appropriate skills -- just direct your helicopters to the oceans and they turn into transports.
All good games. But a few simple adjustments would just really relieve a lot of the small annoyances.
Civ 3 was great fun. I actually installed windows to play it when it came out. I remember one game, I was doing well, better than my neighbours, then oil appeared on the map. But not in my terrortry. This required an unprovoked war of expansion into a neighbour, and quickly, to gain control over this critical resource.
Call to power was quite good too - with undersea, space, and future tech.