I like everything after Hammerheart and of course Nordland I & II.
Just Twilight of the Gods, is a different league, with all the rest and with most of Metal releases though the years. It talks directly into my heart this album.
I remember in the few years that followed his passing, rumours abounded that a vast trove of unreleased treasures sat in the Black Mark archives. Then the '..In Memory of Quorthon' albums were released in 2006, containing no new material. Now that label owner/producer/father Boss Forsberg has died too, it seems that this compilation is the final word on a fascinating discography (although an in-depth book is apparently on the way).
In the case of Quorthon, release of new material isn't really necessary imo. He is such an inspiring person, his legacy will be living for years to come, seeding infinite dreams and inspiring new artists. To me, he's in par up there with Lemmy, Ronnie James Dio & Bill Tsamis (Warlord) to name some of my Metal "saints".
EDIT: Listening to Bathory all day as I work now. Dark outside, a city in silence. His hypnotic riffs deliver magic to my room, awesome. Thanks for that!