Rome: Total War
One of the current highest-rated games, considered by many as the best real-time strategy yet.
The game is a lot of fun, and is very detailed both in its graphics and in gameplay. It's very satisfying to lead a huge army, using ancient tactics, against another huge army, watch the carnage, and come out on top. Think "LOTR: Return of the King" scale battles (thousands of troops), each unit within its 'platoon' independently animated, each platoon under your control.
Anyways, for anyone that's a fan of RTS's, this one's worth looking into.