Viking-era Bathory and "Epic metal". What is it?

What's the deal with this stuff? I'm not too sure what the limits of the genre are.

First contact I had was with the awesome Atlantean Kodex, which is described as "epic doom metal", which has heavy rolling riffs with rather power-metal-style operatic vocals. Then I listened to While Heaven Wept which is similar but seems to go a bit further into the sugary productions of power metal (though there's still a solid foundation of doom). Recently I got into viking-era Bathory (Hammerheart - Twilight of the Gods - a few later albums), which is apparently the invention of "viking metal". I've heard that Manowar is also related, but I'm not too sure which songs are relevent to this genre (I've listened to some of them but not all).

Atlantean Kodex is basically the same sound as viking-bathory. Are epic (doom) metal and viking metal different names for the same genre? Is bathory epic doom, and is Kodex viking? Viking metal is described in wikipedia as a subgenre of black metal, but it seems completely different from what I've heard. And it's clear that viking metal is not just metal with viking lyrics like Amon Amarth.

It seems to be characterised by grand, 'epic' songs with long rolling riffs and tales of journeys through ancient magical lands. It's orchestral and symphonic in composure but not in instrumentation/production, which tends to be quite raw and traditional. I'd say it's very hypnotic and atmospheric too.

I've only heard these few bands so I'm just trying to get my head around it. Know any more bands? Is the genre very big? Are my descriptions accurate? I fucking love the sound and need to know more.

Edit:

http://en.wikipedia.org/wiki/Viking_metal

The article here mentions Bathory as the founder of the genre, but the descriptions of sound seem completely different to what I'm hearing in Twilight of the Gods. It also mentions the band Enslaved which I see has been posted just an hour before me, and yet it just sounds like typical black metal.

Viking metal is a subgenre of black metal characterized by its chaotic and noisy sound, slow pace, use of keyboards, dark and violent imagery, and lyrical themes of Norse mythology, Norse paganism, and the Viking Age.

"Slow pace" is right, but "chaotic and noisy sound" isn't. What's goin on?!

Edit 2:

I've come to the conclusion that Bathory is basically melodic heavy metal. As is AK. The atmosphere in the bands here isn't limited to a specific sound or subgenre.