That's an interesting idea, I wonder if we might see any patterns in the albums we constantly find ourselves listening to. I love In the Nightside Eclipse, but find myself listening to it rarely;
In no order of preference:
1) Sacramentum - Far Away From The Sun
2) Suffocation - Effigy of the Forgotten, Breeding the Spawn and Pierced from Within
3) Therion - Beyond Sanctorum and Symphony Masses
4) Incantation - Onward to Golgotha
5) Immolation - Dawn of Possession and Here in After
6) Darkthrone - A Blaze in the Northern Sky and Transilvanian Hunger
7) Varathron - His Majesty at the Swamp
Summoning - Minas Morgul and Oath Bound
9) Graveland - Thousand Swords and The Celtic Winter
10) Gorguts - Obscura
11) Infester - To the Depths (In Degradation)
12) Rotting Christ - Thy Mighty Contract and Non Serviam
13) Bolt Thrower - For Victory
14) Amorphis - The Karelian Isthmus
15) Necromantia - Scarlet Evil Witching Black
16) Burzum - Det Som Engang Var
17) Immortal - Diabolical Fullmoon Mysticism and Pure Holocaust
Yet I hold other stuff that I don't listen to more often in higher esteem than some of these albums. Enslaved, HLTO, Demoncy, Profanatica, the aforementioned Emperor etc. etc. Looking at the list now I guess there are some common identifiable threads, but I'll leave that to others to decide for themselves. It's a rather uncontroversial list.