I'm a huge fan of their stuff because of the way they blend
so many disparate genres into one very cohesive soundtrack. I mean they literally are a "Diablo. Swing. Orchestra." - death/thrash metal with swing beats and orchestral instrument backup? The only thing they don't mention is that they've got an opera singer for a lead.
If you're still on the fence about giving them a try or buying a few songs to support a very small band, I would recommend this band if you're a fan of Nightwish at
all.

I wouldn't put them in the same genre, in fact, I don't really consider DSO to fit into any particular genre very well, but I know that I was a HUGE fan of Nightwish and now I'm a HUGE fan of DSO.
