⭐⭐⭐
Short review:
A confusing, purposefully dense book that forces you to decide if it's worth the 10-book journey.
Long review:
SPOILER ALERT: I ended up reading the whole 10 books, no matter what I say here at the end. But my original opinion stands, so I thought it useful for new readers.
What a difficult book to review... I liked it and read it at a brisk pace, which should indicate I liked it a lot... but I can't in good conscience give it more than a 3.
The main issue a lot of people seem to have with this book is that it just throws you in media res to the deep end of a fully-fledged world and that it's hard to make sense of what's happening. That's partly true, though a lot of books are very successful at it. This one isn't, mainly because it's all over the fucking place. First of all, the author seems to suffer from awesomeitis, that is, he wants to put all the awesome stuff he thought of into this book. That's why you end up with a dozen viewpoint characters, plots and foreshadowing that won't pay off until the latter books in the series (hopefully, as I haven't read them) and a sense that all characters (with the exception of Kruppe) are pretty much alike. He doesn't stop to develop any character at all, even Whiskeyjack (who seems to be one of the main characters) doesn't get any development or even insights. The ones who do (Captain Paras, Adjunct Lorn, Rallick Nom, Crokus) don't benefit from the attention, since their "character arcs" are so overt and clichèd that you end up kind of hating them. Thus, the ones that tend to retain the reader's interest are Whiskeyjack and Quick Ben (since they get little direct exposure and seem slightly more nuanced) and Kruppe.
The strong point, as should be expected, is the plotting and worldbuilding. Given the 10-volume nature of it, I can't really say if the worldbuilding is tight or just a big old mess, since we mostly get name-droppings and hints in this book. There seems to be a magic system that appears more complicated at first than it probably is (due mostly to not bothering to explain any of it, due to the author's "hatred of exposition", as he says in the prologue. It's funny he doesn't realize he uses exposition a lot of the time, only he focuses it on things that needn't be explained, while basic things like the magic system, the extent of the empire, little things like that, get no explanation). The plotting is mostly tight, with all the various strands converging at the end of the story, in a very long climax that mostly pays off (though you can see some of the twists a mile away and some of the others feel too "deus ex machina").
Still, as I said, Gardens of the Moon is an enjoyable and brisk read, though it feels at times like an overly-complicated telling of an AD&D campaign more than a well-written book. In this and due to the meandering, unfocused storytelling, Erikson seems light-years behind other modern fantasists like Brandon Sanderson, Patrick Rothfuss and others. He seems "old-school", which shouldn't be the case, but compared to G.R.R. Martin, for example, he seems positively a product of the 80's or 90's. He seems much closer to Robert Jordan and his messy, meandering ouvre than to any of the authors who are revolutionizing fantasy.
I'll probably give the second book in the series a try, to see if it's on an upward swing, but won't read the full 10 volumes if it seems to be a "Wheel of Time" in the making...