Hunt might be one of my favorite games ever and the fact that the sound design is interwoven with the gameplay so perfectly is one of the reasons. Also all of the guns sound amazing.
And because you can be a bit slower and ‘tactical’ (not sure if this is the right word) than in most MP FPSes means even an old fart like myself can enjoy it. It doesn’t quite center around being fast at clicking on enemies heads as much as more fast paced shooters does.