Whole soundtrack? Splatoon 2 probably. I like it a whole lot, and don't think it has a single weak track.
A lot of them in other shooters are serious and usually hellish tone; mixing sacred/ heavy metal. And while I like a lot of the electric guitar and bass it becomes somewhat uninspired and one-note for a whole soundtrack. If I take some of these games (Dusk, Wrath, D00MIV/ Eternal) overall the OSTs sound too similar, could even be mistaken as remixes of each other.
And even then I think CastleVania has them all beat (not a shooter) for blending Sacred/ Metal_
I don't need a soundtrack. The cries of my enemies as I score those headshots like BOOM headshot BOOM headshot BOOM HEADSHOT is music enough to my ears.
That and Perfect Dark. The sound of the Farsight when your shot rips through the walls as your multiplayer enemies sitting next to you on the couch beg for mercy! Their cries of "that's OP!" are like little violins playing the world's saddest song.