Fellow Opeth Fans:
I never really considered it weird that Martin played a Jazz. I've always considered it to have a very versatile tone that works in most musical situations. As stated, I think he always plays appropriately, adding rhythm as well as melody.
I've been a fan of theirs since about 1998, and I've seen them live 3 times. I'm pretty much a fanboy.
I found a really great interview with their previous bassist Johan DeFarfalla (Found on Albums: Orchid, Morningrise)[Invalid or Expired Link Removed]They actually contact Johan, He is now a politician in Sweden. Michael actually adds to the forum discussion also. I highly suggest check in it out.
If you haven't heard the bass playing on Morningrise I strongly suggest you check it out, it's probably their best album in terms of bass playing.