I was a little reluctant to give my own input here because, frankly, you should make this decision for yourself. However, one thing I've learned through ANUS is that making an effort is ALWAYS more useful than not, even if you may be wrong. In that spirit, here is what my own decisions would be:
Definitely keep. If you haven't come to like, or even perhaps love, these albums yet, ignore them for a while. Don't try to make yourself like them; instead, let them sit, silently, until one day you get a random urge to listen to one of them again. You will likely end up being surprised:
Auzhia - The Key of Throne
Averse Sefira - Tetragrammatical Astygmata
Krieg - Destruction Ritual
Mutilation - Remains of a Ruined Dead Cursed Soul
Profanatica - Profanitatis de Domonatia
Sacramentum - The Coming of Chaos (but I really really love Far Away from the Sun)
Veles - Black Hateful Metal, The Triumph of Pagan Beliefs
Additional notes: That Avzhia album is the best of this bunch - that thing is incredible, I have trouble understanding how you could want to delete it. Krieg fills a very specific niche, if you're not in the precise mindset required to appreciate it, it will seem dumb. Sacramentum's death metal is fantastic, I had some trouble liking it as well only because
Far Away from the Sun made it seem dull in comparison - take the two albums at face value instead and they should seem much better. As was already pointed out, Veles isn't an insta-like; once it seeps in, though, it is for good.
These are all good, some even very good, but they will never be considered amazing. They're worth keeping to a degree but don't expect any miracles. You could probably afford to lose these, but they do hold their own charm in the end:
Absu - Tara
Bathory - Under the Sign of the Black Mark
Blazemth - Fatherland, For Centuries Left Behind
Enslaved - Frost (Vikingligr Veldi is awesome, but this.....)
Kvist - For Kunsten Ma Vi Evig Vike
Manes - Under Ein Blodraud Maane
Moonblood - Blut Und Krieg
Naglfar - Hunengrab Im Herbst, Srrontgorrth
Sorcier des Glaces - Moonrise in Total Darkness (although Snowland is really great)
Zyklon B - Blood Must be Shed
Additional notes:
Barathrum: V.I.T.R.I.O.L. is Absu's best, and also their darkest. The following two albums and the
In the Eyes of Ioldanach EP are fantastic as well.
Tara is good, but not on the same level as those four works. I find
Under the Sign of the Black Mark to be the weakest of Bathory's early work, so I get why you're considering getting rid of it, but it nevertheless maintains its own distinct character within his catalogue. The production of the Blazemth works is pretty hilarious, but the music itself is still good.
Frost is, as you said, a pale comparison to Enslaved's debut, but like
Under the Sign of the Black Mark it is good for its own reasons. Every single one of the other bands have value, but nothing close to the bands in the first list.
These are
OK. Not great, and not even necessarily "good." I myself would probably give them a few weeks each at most, but I wouldn't say they're immediately horrible. Still, in the end, delete:
Blut aus Nord - Memoria Vetusta 2, The Work Which Transforms God (I quite like Ultima Thule, but these albums.....)
Dissection - The Somberlain, Storm of the Lights Bane
Gorgoroth - Destroyer
Nazgul - De Expugnatione Elfmuth
Nazxul - Iconoclast
Negative Plane - Et in Saecula Saculorum
Pensees Nocturnes - Vacuum
Primordial - To the Nameless Dead
Satyricon - Dark Medieval Times
Vinterland - Welcome My Last Chapter
Windir - Arntor
Additional notes: Blut Aus Nord's best is definitely, as you already know,
Ultima Thulee - but even that would only be included in the second section above, if at all.
Memoria Vetusta I is decent as well, certainly better than
II, but in the end you're still not missing much by ignoring it. Nazxul isn't bad, actually, and I think I'm in the minority by finding their new album better than their "classic" old one. The new one might be worth placement in the second section above, actually, but probably not.
A pile of AIDS. Clean out with steel wool ASAP or risk infection:
Cobalt - Eater of Birds
Coldworld - Melancholie
Dark Tribe - In Jeraspunta
Darkspace - Darkspace 2
Drudkh - Firth Four Albums
Krallice - Krallice
Lunar Aurora - Ars Moriendi
Nachtmystium - Eulogy 4
Nachtmystium - Instinct Decay
Wolves in the Throne Room - Diadem of 12 Stars (I listen to Two Hunters sometimes)
Wyrd - Huldrafolk, Heathen