I wanted to do a quick post for my own benefit really. I've been reading 'Lanark' by Alasdair Gray for about 4 months now. I'm not a particularly slow reader, in fact I've been flying through it because its so interesting, which is why it's taking me so long...going back and re reading several passages.
There are complex themes, a lot of which are centered around religion but the format and general plot are somewhat indescribable so I would recommend giving it a read.
Also it's on The Observers Top 100 novels to read list.
Gray produced several illustrations for the novel and on further research I found some more great stuff. I LOVE that his work has spanned so many decades and therefore won't have been influenced by the current saturation of the illustrative scene, with so much material looking the same and each theme and style being indistinguishable from the next.
Here's a link to his blog:
http://alasdairgray.blogspot.com/
