Frederik Pohl is a good writer, but in this book he outdoes himself completely. Gateway is a masterpiece, a dark psychological tale set upon a background of mysterious alien technology. The aliens are genuinely alien (though later sequels take away some of the mystery, and inevitably disappoint), and the characters are brilliantly drawn. There are several sequels to this book; they're decent, but don't match up to the original.
When I started reading this book, my first reaction was, "Wow, what great atmosphere!" Egyptian magic, Coleridge, eighteenth-century England, secret societies... atmosphere abounds. But the thing about atmosphere is, it works well for the first half of a book, when the writer can get by with obscure intimations; but eventually, the book has to let you know what's going on -- and that's the point when many atmosphere-heavy books dissolve into an inchoate and incoherent mess. Because while it's easy to throw together a bunch of really cool elements and hint at secret plans and intricate plots, it's a lot harder to tie all those disparate elements up with all those ominous hints; and it's harder yet to make the revealed story live up to its veiled promise.
I stress the difficulty of this task, because it's all the more remarkable that Powers pulls it all off. The time travel, the mysticism, the historical figures -- it all works. When Powers finally pulls the veil away, what's underneath is just as intricate and rich as the reader has imagined -- and it makes perfect sense. That's an impressive trick indeed. This is the kind of book I really enjoy: it's complex enough to rise above the level of fluff, but still possesses the pace, wit, and joie de libre that make fluff so attractive.
It's very tempting to compare Pratchett to Douglas Adams; I have no intention of resisting this temptation. Both, after all, write humorous genre fiction, and both are British. Nevertheless, Pratchett's style is very much his own. The Discworld books, while being staggeringly funny, have a depth that Adams lacks. Pratchett possesses a deep insight into the human condition, particularly in his later books. What's more, his plots actually work. Adams' plots are just joke vehicles, and are completely nonsensical; Pratchett's plots are real, complex, and subtler than you realize.
Don't be scared off by the sheer number of these books; each book stands alone, plotwise (though by the time you reach Lords and Ladies, it helps if you have some familiarity with the characters). And remarkably, there's no degradation in quality in the later books; I consider his later books to be his strongest, in fact. Finding earlier books in the series is rather difficult in the US, but well worth the time. (For those who are hesistant to tackle a series this size all in one go, I recommend Small Gods as an accessible starting point. It's a completely stand-alone book, so you don't need to be familiar with characters from the other books; more importantly, it's very good. While the first few books in the series don't possess all the virtues of the later books, this is about as good as they get -- if you don't care for Small Gods, Pratchett's just not your cup of tea.)
One of the more impressive things about the Discworld books is that Pratchett's been able to write as many of them as he has, while still staying fresh and original. Unfortunately, the freshness and originality is starting to perceptibly dwindle at this point. Both of these books feature familiar characters in familiar situations dealing with familiar themes. They're still excellent books, and are at least as good technically as earlier books in the series; but there's nevertheless a distinct feeling that we've been here and done this before. (Fortunately, it appears that Pratchett is noticing the same problem: his next book will feature new characters.)
I had very high hopes for this book -- the last few Discworld books had been a bit stale, but this one promised to freshen things up with a new main character. Unfortunately, it only partially delivered. There is a new main character, yes, but the whole story is set in the familiar surroundings of Ankh-Morpork, and the familiar characters of that city -- the Patrician, Dibbler, the guards, the bums -- are all prominent in the book. The result is that the book feels a lot like the other Guards books, new protagonist or no. Even the plot, which focuses on the consequences of a new medium, has echoes of Soul Music and Moving Pictures (an allusion to the events of those books is even made). The end result is a book that's very good, a perfectly fine Discworld book, but not the fresh, new direction I'd been hoping for. It still gets a star, but it's a near thing.
I was actually a bit nervous going into this book -- was Discworld getting stale? Would Pratchett be able to break out of what I've viewed as a recent slump? The answers, to my relief and delight, are no and yes, in that order. It helps that this is book features Death, who continues to be one of my favorite Discworld characters, but it also helps that it's just very good. Sure, there are some themes that are obvious echoes of previous Discworld books, and the basic plot in outline is not radically dissimilar from, say, Hogfather; but apparently I'm not as fixated on freshness and novelty as I imagined I was. I'll settle for quality.