Civ III, IV, V ... all good games but still no where near as great as Civ II was.
Civ IV is a much better game than Civ II once you move beyond the stock game and get in to all of the great mods the modding community has made for it. Unlike Civ II, the game mechanics can be completely changed by user-contributed mods.
For example, one user named "Cephalo" made a map script (a mod to change how Civ IV makes maps) called "Perfect World" that makes incredibly beautiful earth-like maps; Civ II's random map generator does not hold a candle to it. Indeed, I have taken this mod and made a "meta-mod" (mod of a mod) of it with more user selectable parameters and map types.
As another example, I have been playing a mod for Civ IV called "Legends of Ancient Arabia" lately. A few days ago, I realized the original designer made a mistake by allowing an easy win game-breaking strategy in the mod. I was able to, via Python scripting, patch this bug by limiting how many times a player can build a certain unit. Even though the Civ IV designers never envisioned having a per-player limitation for a unit to be built, I was able to add such a limitation to the game. That's something that never was possible with Civ II.
Factory stock Civ IV may not be as good as Civ II, but once you dive in to all of the mods out there for it, it is head and shoulders above Civ II in terms of flexibility and replayability.
Indeed, it would be feasible to make a "Civ II gameplay" mod for "Civ IV"--though, I should point out, no one has bothered to make such a mod.
- Sam