I'm not quite sure if the Decemberists really qualify as shrill, though in its more subtle way 16 Military Wives (song and video) did achieve some level of understated sophisticated shrillnes.
The new CD, the Crane Wife is quite good. It seems to be a bit more of a cleaner recording than some of their earlier stuff, with individual instruments coming through more distinctly. In some ways it's more accessible than their previous recording, but it also has some odd influences. There's one song which would be at home on a Steve Miller Band CD from the 70s. Another one which could've been pulled right off of a Jethro Tull CD. And I can imagine big chunks of the epic title tracks being performed by Yes. Perhaps The Decemberists are trying to make the world safe for progressive rock again. Don't tell Steve Simels.