The sound design of a game doesn't only include its soundtrack (though it is a pretty solid chunk). The sound effects of slashing, explosions, punching, walking, etc. must also be satisfying.
Meteos is a personal favorite in this regard. With perhaps one exception, the game arguably doesn't have a "real" soundtrack that plays during the actual gameplay. It's just short loops that constantly change based on the situation, punctuated with the sounds and jingles made by matching pieces in regular gameplay. But they come together in such a way that the game doesn't even need a "real" background track; the sounds alone are more than good enough since every move you make causes a satisfying audio response.
What makes a game's sound design good for you? Post some examples of games with good audio, and maybe their sounds/music too.