Paradox Interactive has been making excellent grand strategy games for a long time, and now it's both convenient and cheap to check out almost their entire Europa Universalis series.

Carve out an empire from the smallest nation, and using diplomacy, war, and religion, ensure your supremacy on the face of the earth. Although I wish this pack also included Rome, I suppose we can't have everything.

So if you have around 5 years to play these games, then I would completely recommend them. They will keep you occupied for much longer than that, and will continue to surprise and amuse you with little oddities like AI Byzantium somehow lasting until the end of the game.