There's a pretty clear trend in the games I've loved and the quality of their soundtracks. For me, sound is just as big a part of the experience as anything else, but I'm not sure a great soundtrack could redeem a game if I can't find anything else worthy of my time in it. I could always just get the soundtrack instead.
NieR would be one game where the music kept me playing, even though I felt the first half of the game kept dragging on and on without anything happening. I'm glad it did, because it was totally worth it. Oh, and Chaos Rings!
I guess music can work as a sort of a buffer. Nowadays I have too many games and not enough time to play them all, so I tend make pretty hasty judgements on whether I want to continue playing or not. No game really hooks me as soon as I put the disc in anymore, but if the music is really good, I'm more likely to play the game long enough to warm up to it. But if the game is rotten all the way through, it'll still leave a bad taste in my mouth.