Unique perhaps in his sound but technically it's just the usual (and even if his voice is unique, many punk bands have unique voices as well). Don't get me wrong, I love NOFX. Went to a couple of festivals just because they were there. But there's been tons of bands like them. Just look at all the Fat Wreck Chords samplers.
Edit: Love their Ska vibes, but that has been done too. Still kicks ass. LOVE their lyrics.