ah nice. Yeah they are basically the fathers of 'epic doom metal', taking up the doom metal flag from sabbath and adding more operatic/symphonic nuances. Messiah Marcolin was by far their best vocalist imo. He had various stints with Candlemass. The main albums that he sung on were Nightfall, Ancient Dreams and the self-titled, Candlemass album from 2005.
Hopefully these album playlist links work for you. They might be region-locked for the US if you aren't located in the US :-/