Old school Finnish dm has one of the coolest sounds of any style. It is weird and original without resorting to awkward riffing that doesn't flow. Exaples include:
Amorphis - The Karelian Isthmus
Adramelech - Psychostasia
Demigod - Slumber of Sullen Eyes
Demilich - Nesphite
Funebre - Children of the Scorn
Old school Finnish death metal alone makes a case for old school dm in general, without mentioning all the other great European and American dm bands of the "first wave" of dm.