Tough question, as I'm sure everyone can attest to. Games these days are really doing great sound design, and the music we get for triple A games is sometimes flat-out amazing. Not that you need a modern triple A budget to do great music, though. The early Sonic games on the Genesis had a lot of sweet tunes. The music from my favorite '90s game, Heretic, is really awesome. In more modern terms, Shadow of the Colossus has not only amazing music, but a unique sound I've never heard in any other game.
But the only game series that has really inspired me with its score is Mass Effect. It's just one more reason to love my favorite games. From the synth sounds of the first, to the larger and more exciting themes of the second, to the sombre, portentious tones of the third, each game does musical cues and aural atmosphere as well as any media presentation I know of. Everyone who worked on these games, Jack Wall, Sam Hulick, Clint Mansell, whoever else, everyone was doing incredible work. I listen to their music all the time even out of the games' context. It's just a fabulous experience for me.