There are a lot of clean vocals from Aaron Turner on this CD in addition to his growls and screams. The songs are epic, beginning with just a few instruments and vocals before adding more instruments and more intensity. They have a definite ebb and flow, with the vocals being followed by lengthy instrumental passages.
Groups like Isis aren't tied down by conventional song structures, which makes them complex and interesting. On the downside, the lack of traditional hooks and choruses makes it harder for songs to be memorable. It's one of the those CDs that while you're listening to it the first time is very impressive and compelling, but afterwards it's hard to remember anything specific about the songs, just that they were good.
But with a few more listens you begin to appreciate the depth and complexity of what's going on, and discover that there actually are some very memorable things about this CD.