I've been playing this game about five to six hours a day for the past couple of weeks (eep). Nominally it's a Minecraft server, but its mods are pretty wide-reaching and it's awesome enough on its own terms that it really warrants its own discussion.
Essentially, what differentiates it from regular Minecraft is that its mods allow players to protect against property damage (by allowing you to reinforce individual blocks and making it much harder to destroy them) and encourages cooperative effort (there are "factories" that are expensive to build, but pay for themselves by making certain processes, like ore smelting, more efficient. Because the initial investment is high, one person can't build all of them with his own resources; community effort is needed). Unlike Minecraft, then, where monuments are easily knocked down by griefers and pvp is rife, Civcraft is much more focused on city-building and trade. There are a couple of other important mods, too (one provides the mechanics for a criminal justice system, the other changes the way crops grow).
Subreddit.Map. (A bit outdated).
My handle is dhokarena56, and I'm actually starting a settlement of my own in the northern section of the map. Shoot me a note in-game or as a PM here if you're interested.