I love it when a four-book series comes together.
Of course, with Tad Williams, there's rarely any doubt that it will come together in the end, just like there shouldn't be any doubt that the "third and final" book will grow so huge it'll spawn a fourth book. Williams always seems to have a good germ of an idea driving each of his big series that you don't really expect. He's matured in his craft with this series, although I still feel like many plot points are made just to tweak the legacy of Tolkien in certain areas: for example, all families are dysfunctional in some way so let's make the central family dysfunctional in some 21st-century way. In many cases it's a nice chance of pace but sometimes it just seems gratuitous, change for change's sake. But really, every author in this genre is forced to keep some orthdoxies while choosing certain heterodoxies, and which should be which is ultimately a matter of taste.
The one thing that bugs me about the series is its theology. It's a polytheistic universe with at least three major cultures. In fact, one of the most confusing things about the series is that the gods all have three different names and the myths are all slightly different, so it's very hard to keep track of when all you have are fragments in the first place. I like the concept and find it an interesting take on our three faiths of Judaism, Christianity, and Islam. Unfortunately, the underlying reality of it all reads as poorly thought out. Williams seems interested only in the question of whether the gods are, or are not. Not to spoil too much, but it turns out the gods are (in a 21st-century kind of way, but really, they are). And pretty much this is the extent at which you're left at the end of the book (with some hints as to how gods, ahem, resolve conflicts, that is, fight). Only one god really speaks, although there are hints of others, and those hints may be my favorite part of the series, especially near the end. You know, if you're gonna be polytheistic, go and be polytheistic and show us what it's like and how it works. In this sense American Gods by Neil Gaiman still wins my award for "excellence in polytheology." Williams just isn't interested in that aspect of his universe, although it drives everything else, or maybe it got edited out.
Despite this, Williams puts on a writing clinic showing how to juggle at least a dozen different major characters and plotlines, and how to shift scenes and (mostly) keep the story moving. He introduces some good ambuguity and true tragedy into a genre that desperately needs it. This is undoubtedly the best-written of all his books, and it's as well-plotted as any.
I suppose it ends up a bit like LOST for me: excellent at juggling multiple lines and telling a story, but what story is being told ends up not being fleshed out as much as you want. Regardless, I'll happily take it.