A good way to tell a group's credibility is to observe how they stand in their epic "in front of a ruin or some other badass thing" pictures. And these guys know how to stand. look at them. Yeah I wouldn't fuck with them.

Bolt Thrower are a death metal group from England that have the catchiest, awesomest riffs and song titles like "Anti-Tank (Dead Armour) and "Remembrance." Yeah they're war themed. Makes them even more badass and over the top. If you want good dm then here you go. I suggest starting with Those Once Loyal.

War Master
IVth Crusade
Those Once Loyal
For Victory