Illyria features a progressive post-black, post-hardcore, metalcore mashup with elements of other genres, including indie and sometimes jazz. I love the use of nature sounds incorporated into the music. I also love the post-black metal influence, which is most prevalent in Illyria's eponymous album.
My favorite track from the Illyria album is "Wonder." It showcases the best of Illyria, and includes a delicious melodic riff at the end.