[ralfd]

For me (subjectively) Civ 4 was the best civ. It has (objectively) the more challenging AI/difficulty.

A hardcore gamers view in what went wrong woth Civ 5:

http://www.sullla.com/Civ5/whatwentwrong.html

[mercer]

I never managed to get back into Civ after playing Alpha Centauri (so Civ 3?). Did something change/improve, or is it possible that I just preferred AC and didn't like how Civ changed after CivII?

[Certhas]

I've played every Civ game since the start, and I get what the critique is going for, but honestly, just don't play ICS style games then.

If you don't, then the game is nicely balanced and a lot of fun. Lot's of great mechanics. And the idea that you can't be effective at the game unless you succumb to ICS is nonsense. Here is a turn 196 Science victory with one city:

https://www.youtube.com/watch?v=lx_PZPZhHMQ

[mihaifm]

Civ 4 has some stellar mods, and I think to this day it has a larger modding community than 5.

I haven't followed the modding for Civ 6, but it looked quite modder-friendly when it launched.