I've listened to a LOT of videogame music in my life, but my favorite videogame soundtrack is one that many people will find an unexpected choice.
I consider Final Fantasy XII to have some of the most well composed videogame music ever. The tracks are very different from the Electronica/Orchestra Fused Compositions of traditional series composer Nobuo Uemetsu, Final Fantasy XII's soundtrack sounds right at home next to John Williams' classic Star Wars Score and evokes a "space opera" feel that gives a unique flavor to the game and helps set it apart from other entries in the series.
The best tracks are as follows.
Speecless Fight - The battle theme of the bounty hunter Ba'agamon and his cronies is a percussion and brass heavy cascade of tribal beats with the occasional piano interlude. It is excellent because it evokes the savagry of the character and the desperation of the first encounter it is utilized in.
Here's an excellent pistache of the best battle themes from the game...
The Battle for Freedom - The final battle theme of the game, a long, sprawling battle theme with an intro that moves into a desperate battle theme and then morphs into a high energy heroic battle theme. Very suitable for the epic final confrontation that it frames.
Other tracks are used effectively to convey the energy of any given scene and give life to many of the various factions involved in the game, such as the theme of The Empire, which is thematically similar to John Williams' Imperial March, however it feels more like an homage than a cooption, as the two are very different in the long run.