Well.... let's say this:
I keep spinning their very first album. Yeah, it's a bit less polished, a bit less accurate, a bit looser, but damnit, their riffage is soooo damned good. I've never discovered a band where their first album is so damned METAL. Usually, I get into their later albums. But Roots Of Eternity has such great songs on it. The Flood is a really long song, and it's got, like 15 different riffs crammed in there. It's so satisfying to hear a band do it like Megadeth and Metallica and Slayer used to do it way back when, and yet be fresh and original enough to do it with their own style and flavor.
So go get Roots Of Eternity, and then work forward. You won't be disappointed.
If you are, I'll buy your copy of Roots offa ya!