Indeed both bands you mentioned are Death Metal.
(Opeth also is not Death, but rather Death than black
![Wink ;) ;)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
).
If you want black or black-colored Bands try:
Borknagar(!)
Progressive Viking and Black influenced metal
Dissection
Traditional Metal with BM flavour
![Wink ;) ;)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
Emperor
Like Dissection but with a higher BM-concentration
Covenant(not The Kovenant(!!!))
melodic metal with BM vocals and female vocals
The first album by Arcturus
a bit like Borknagar, just with different atmosphere
If you wand more Death Metal(ish) or Göteborg bands(like Opeth), try:
older In Flames
Dark Tranquility(!)
My Dying Bride