The King of Turn-Based Strategy!
I thought this was going to be my send-off to TBS, the game that finally sent me packing, realizing that the genre was out-of-date. But it has turned out to be extremely addictive; this is the first time I've experienced the hallowed "One More Turn!" syndrome, which I thought was just a myth.
I should warn people, though... this game has, by leaps and bounds, the largest learning curve I've ever experienced. I've been playing for months, and I feel like I've barely cracked the surface. There is just so much depth to this game, but I can see how it overwhelms people. My advice... finish the tutorial (this may take 30 hours!), then dive headfirst into multiplayer. You will get destroyed, but you will learn a lot.
The best way to describe the game is Dungeons and Dragons crossed with 3-dimensional chess. If you can get past the extremely primitive graphics, and the 294 page manual (I've read it three times and I still don't feel like I know much of anything), you'll be rewarded with games that last months (some of them have lasted over two years), battles that are straight out of Helm's Deep, and a tax on every brain cell you have.
Highly, highly recommended for those willing to invest the time necessary to learn the game.