I'm amazed - both by the fact that some (many) people consider this book unreadable, and by the fact that I had never heard of this fine Canadian author.
Common complaints have concluded that the characters have no depth. I guess if you want character-based stories, this book, and presumably its sequels, are not for you - but then I wonder where you're going to find that in modern fantasy. Fantasy is nearly invariably plot-driven — certainly one of the things that draws me to it — and this tale has one of the most intricate plots I've ever read. The characters are not so much one-dimensional as simply sketched. I fully expect the significant characters to be more fleshed out as the series continues: which is exactly how the characters of people you actually meet develop in your own mind.
There's no doubt that it could be difficult to concentrate on the story, especially at the very beginning. The reader is thrown into a world with very few similarities to ours, and it's immediately "sink or swim". Why are people rioting? What is a warren? How, and why, was the Emperor overthrown? As time goes on, we learn some of the answers, but not all, and anyway - far more questions arise! Where fantasy is frequently a simple good-vs-evil conflict, and we almost always expect Good to triumph, in Gardens of the Moon I count at least 8 different "sides" to conflict, none of whom are wholly good and none wholly evil (excepting the Jaghut Tyrant). For limited periods, and limited objectives, alliances are made, and broken, exactly as happens in our world.
I started (and haven't finished) both Robert Jordan's and Terry Goodkind's massive fantasy epics, and got frustrated by both because they had clear objectives — destroy the source of Evil — and at the conclusion of each 1000+ page volume (OK, Goodkind's weren't quite that long), they didn't seem any closer to conclusion. The tales of the Malazan Book of the Fallen
promise to have much more staying power - precisely because there is no obvious target.