I often think gamers and critics alike don't give music enough weight or consideration. The interactive entertainment industry requires fantastic soundtracks for the sake of immersion; great music enhances the experience in a subtle yet crucial way.
And while so many great titles have offered amazing soundtracks, I still think the single greatest music assortment was found in Castlevania: Symphony of the Night . One could argue we've long since advanced and can now implement full orchestral pieces (with no electronic synth help), and popular music is becoming a bigger and bigger staple, but we have to examine this from a bird's-eye view. Hardware limitations shouldn't be a factor.
We have to examine it strictly from a musical standpoint. Is the selection diverse? Are there enough various tracks to suit all gameplay situations? Is it well balanced or do the sound effects and/or voices override the music? Does part of our brain routinely take time out to actually listen to the soundtrack as we play? SotN succeeds on all fronts. There's a surprising assortment of tracks and it's incredible how many can be classified as memorable. I remember the majority to this day.
I think it's the only game soundtrack I've heard that tackles every emotion in the human rainbow. There are pieces for fear, rage, mystery, sorrow, and even awe. Each composition is beautifully arranged and presented. In all honesty, even after all the wonderfully accomplished soundtracks we've had since, SotN is the only game I replay again and again because the music is just so captivating. The gameplay is awesome, too, of course, and the design is almost unparalleled, but the music is the main draw.
How many games can we say that about?