Without going the heavily copyrighted soundtracks (GTA Vice City, GH2, Crazy Taxi etc)... Lumines and Tetris Effect... these immediately come to mind... the music is even more important than the gameplay in these games.
However there were many old games where the soundtrack was the main attraction, particularly on old 8/16bits computers, so i 'll just stop with these two, since the intent really was to put the music front and center to the experience, it was important for it to be good in order to have enjoyable experiences.
I'll however give one other game... Nier Automata... damn the soundtrack was fannnnntastic and elevating the game so much.