The intensity - that's exactly it. It's less intense partly because the hazard is mostly gone - we know that 80% of the characters will never actually die, and that takes a lot of the tension out of any storyline - but also this dilution of focus means the interest is being leached out.

The annoying thing is that this shift could have been done in a way that was exciting and more subtle, Sam and Dean could have been given pivotal roles and still have reduced screen time, but this current crew of writers are either incapable of creating dramatic tension or not being allowed to do so.

And yes, I blame you for discovering the purity brigade ha ha ha!