10. The Elder Scrolls III: Morrowind - Nerevar Rising
The origins of the main themes of both Oblivion and Skyrim can be found in this epic score. The beating drums at the beginning can be found in Skyrim's Dragonborn, and the emphasis on strings has carried into Oblivion's Reign of the Septims, but the climax of Morrowind's main theme wipes both away with an orchestral score that conveys the sheer openness of the game.
The main problem with Dragonborn was that, while epic during the battles with the dragons or fus-ro-dah-ing someone off a cliff, it couldn't really capture the vast expanse of the world. It made for a stirring combat theme, but not an awful lot more.
Whether dungeon delving or jaunting through Morrowind's beautiful landscape, Nerevar Rising makes the player feel like they want to explore the whole world with this song at their back, which is exactly how an open-world game's soundtrack should make a gamer feel.