It's a constant dilemma that bands face, either you become a band like AC/DC who has essentially made the same album 20 times, and people make jabs at you for playing it safe your entire career, or you try to change things up and change your style, and as a result you will get both love and hate for it. There are many ways in which you can change and evolve your sound of course, and the depending on the direction, people will either like or dislike it.
With Opeth, I've said it before, the 70's direction is not something I'm fond of. But I still give the music a chance, and in the same way Heritage was a disappointment for me, Pale Communion is a positive surprise. I don't know if I would automatically love another album in the classic Opeth style either. They've already made perfect albums in that style, so personally I don't think they could top those albums, so I'd rather see them do something else. Again, the 70's thing is not something I love, but at least they're doing something else.