I heard Arcturus 'the sham mirrors' and do not really get the hype, the first song was really good and then a 1,2 other songs were cool but that's it, garm sounds great and musically the album is not all the impressive. I never really though wow this album is just beyond everything. For something labelled Avant-Garde I expected a lot more.
The only two Arcturus that even potentially qualify for being avant garde are La Masquerade Infernale and maybe Disguised Masters (though that album was very hit and miss). For the rest they are a good band but not really as outthere as some people will have you believe. The Sham Mirrors is probably their most straightforward album.