I don't have much time to properly answer the Immortal question? Sorry, I love double entendres!
Anyway, each of the 7 Immortal albums are very different in terms of style, but they all share a very similar flow. Funny how similar it is to Opeth's discography. Once you listen to them its odd how little they talk about Satan, considering the genres they're a part of. Almost all of the albums focus heavily on a place known as Blashyrkh that's full of ice, snow and a dark brooding atmosphere.
To anyone who is new to Immortal I say get
Sons of Northern Darkness first. It's the most developed and rounded. This doesn't mean the others are bad, they in fact kick major ass, but you'll probably appreciate the band more if you start there. The first two albums called Diabolical Fullmoon Mysticism and Pure Holocaust are excellent, though Pure Holocaust is better overall. The third album, Battles in the North, is great but its much more raw, faster and probably harder to stomach if coming immediately from Opeth. Blizzard Beasts is short, fast and more death metal oriented. I'm not all that into it, but its cool. The fifth album, At the Heart of Winter, is a pretty ubrupt switch in their style probably since the guitarist, Demonaz, got acute tendonitis and had to quit. It's much slower overall, but is an amazing piece of work. It's funny i'm writing this now since I just finished that album. Next is Damned in Black, which is probably my favorite. It's fast and more evil sounding and yet still seems to retain the beauty of the band. Last is Sons of Northern Darkness, which encompasses alot of the changes the band has made over the years and also has a very unusual digipack design. According to a couple of interviews Abbath (THE MAN) likes this one the most, yet wishes that two of the songs turned out differently. It takes alot of the melody from At the Heart of Winter and blends it with energy from the first couple albums while having the production value of Damned in Black.
Ok, I hope I didn't bore anyone, but I love this band and I know alot of you'll have different opinions on which albums you like more. Personally, the whole discography is worth buying but be prepared for 28-45ish minute cds. There's no 74 min Morninrise reissue cds in their collection. All of them are available at
http://www.theendrecords.com/omega/ at damn good prices. I bet half of you already know that though.