Anyone with a lot of time on their hands, a heavy interest in this type of game, a fondness for multiplayer, no dislike of math, and a perfectionistic methodical character should check out an email game called Galaxy. (You can find it with "searches", I play a variant called Galaxy Explorer. I recommend searching for "Blind Galaxy" however because Galaxy Explorer may or may not ever run again.)
Galaxy is the best game I have ever found. Easily. No question at all.
The downside (I do not consider this as a downside but normal folks probably do) is that games last typically 6-15 months AND require immense amounts of time to work out each individual turn.
The Galaxy games are text-based, graphic-less, long-term strategy games.
Galaxy is not a game with any flashy effects. A person should consider carefully before joining as the game requires serious amounts of time and effort. (Once the game gets past turn 15 or so, I spend about 15-20 hours per week on it.)
Galaxy games are free, run mostly by veteran players.
One of the main problems with converting a game like Civ to multiplayer is that the turns resolve one player at a time. Anyone who wanted to play an 8-player email game where you had to wait for 7 other people to move would have to be a lunatic. Galaxy solves this by having the moves run simultaneously (in the same way that the board game Diplomacy does). Everyone writes out their orders and then all the orders run at once.