I doubt many (none yet?) will vote vanilla, especially since we finally got our BTS patch.
The new disable Espionage option is a bit wonky, but I doubt I'll ever use that.
The only way CIV could realistically be improved, would be better AI + Trade + Diplomacy - beyond the expected Graphical/Streamlined UI/general game improvements. BTS is by far one of the best games I've played. I'm sure everyone would have their own personal favs.
In no particular order:
Risk II, Hexen, WarCraft II, Warlords III, CIV IV:BTS, Sacred (RPG), the original Dungeon Siege.
I don't game as much as most, and generally prefer older games that focused more on gameplay (substance) over graphics (candy). Unless Sid really f's up, CIV (or possible successors) will find its way onto any Top Games of All Time (list) for many years to come.