There's a lot of metal out there which is garbage. Guns Drums and Steel takes after the best Scandinavian metal traditions, the non-extreme variety anyway. It was done tastefully and fits in very smoothly with the game's atmosphere.
Well, garbage is subjective, but metal is definitely a very vast genre. The notion that someone would hear some, dislike it, and never find out that there's other kinds of metal they would have wound up liking is certainly credible.
Case in point, I had a pretty negative opinion of metal until I discovered the more melodic kinds - which is pretty much all I listen to anymore.
Naturally, I like the DLC and I intend to buy it alongside AoW.