Yes, its true they do cop a bit of shit every now and then.
Mainly, Opeth dont follow the standards of 'metal'. Steven Wilson calls it "that level of sophistication" but he's a dickhead so who cares. Quite frankly, the fact that they dont write agressive music, and include melodic and accoustic interludes. This, as any devoted death metaller or thrasher will tell you, is for pussies.
That is all.