#15 Far Cry 2
Far Cry 2 is set in a fictional and nameless central African state that offers a diverse range of geography including deserts, jungles, and savannas. It's populated by warring factions, mercenaries, and the civilians (and native wildlife) caught within the crossfire.
Touted as a realistic game, you'll have to navigate through the terrain with a map that you'll actually have to stare down at. There's no heads-up display to tell you where to go in this game, so exploration is as real as it gets.
I should add that the journey the player undertakes is not unlike Joseph Conrad's journey into the Heart of Darkness.