"Ghost River" - Nightwish.
I think the heaviest I'm ever going to go, it's an amazing tune, the introduction and pretty much all of the instrumentals are epic, as are the verses and the chorus but the prechorus (growling/screamo) is really hard to get used to, and I'm not sure if I ever will. This is probably some of the heaviest Nightwish there is. I'm really getting into them now, never really liked any metal before at all (with the possible exception of Linkin Park, but there I avoid most of their really heavy/ screamo tracks) but NW is so versatile with so many different genres, I've heard Jazz, acoustic rock, indie, classical music, film type music (very much this) and even a smidgen of pop influences in their songs. They've got to be admired for that.
(ETA: I forgot Folk/Country and Celtic.)