Don't listen to the idiot children who say the game is "too hard"; it is DIFFERENT. Read on to find out why.
You take control of a single civilization (America, Germany, Russia, what have you), all of whom have specific bonuses and unique units, and guide it into the future -- and hopefully to victory. There are a variety of methods by which a civilization (hereafter referred to as a "Civ", for brevity's sake) may achieve victory; be it a Diplomatic victory, Economic victory, Military victory, or one of a couple of others. The key is to PLAN on which path you want to pursue and how you will prevent your enemies from winning before you do; it isn't enough to simply pump out military units and try to steamroll your enemies. Generally, every Civ is uniquely suited to excel at one victory methodology over the others so choose carefully.
Thankfully, the game comes with an expansive and encompassing "Civ Encyclopedia" (I'm paraphrasing, as I've forgotten what it's actually called) that will tell you exactly how how the very involved tech-tree flows, how military units function in combat, how diplomacy and religion are executed, and, probably most importantly, how the game's victory conditions can be achieved and, by inference, stymied.
Also, and here's the icing on a cake that's already made out of pure "awesome", the game is narrated by Leonard Nimoy! Every time you research a technology you'll hear Mr Nimoy's erudite commentary about it. Not surprisingly, this really adds to the whole experience regardless of whether or not you've even ever seen an episode of Star Trek (as was the case with me).
In summation: this is a game for someone who wants to really think during their gaming session, and to see the fruits of their careful planning play out in the most rewarding ways. If you're ready for that, then you will love this game.