Bolt Thrower are a great band, but I wouldn't see them as essential. I mean, they play good fucking death metal, but they didn't revolutionise much. Then again, I'm a bit of a philistine when it comes to DM, so fair enough. Same again with Deicide: yeah, it's fun to sing along with 'Blame It on God' or 'Scars of the Crucifix' but it's pretty mundane stuff. Nile though, fuck yes. Behemoth as well, in the same vein.
Helmet I could never really see the appeal in, but over-all I suppose I just don't really like the classic 'american metal' sound that much. I mean, I like swampy deep south sort of stuff, in particular Acid Bath and Danzig, but also Alabama Thunderpussy and the whole southern sludge scene a-la Eyehategod to an extent, but not so much say, Pantera, or a lot of Bay Area thrash. My main hots have always been mainly for British and Scandinavian shit.
Also, am I really the only person alive who prefers 'Panzer Division Marduk' to 'Heaven Shall Burn...'? Yeah, I know it's fucking heresy, but I can't help it, Panzer Division is so fucking fun.