I find that for a few weeks at a time, I will listen to nothing but Opeth. I doubt that I will ever get tired of Morningrise or Blackwater Park. When you consider the range of musical styles along with the depth of their material, it's very difficult to get tired of them.
On the other hand, after listening to them for a few weeks, I won't touch them again for a while. Opeth is just so different from all other metal bands that I find it really hard to mix them together. When I crave Opeth, I get borderline-obsessive about listening to them. But once that passes, it's nice to put the CDs away for a while, knowing that I will come back soon enough.