A collection of excellent stories but which feels, on the whole, a little underwhelming or unbalanced. Each story is a true exercise in world-building, setting, and Big Ideas, which probably helps to account for the piece's longer lengths. Fortunately, Egan's exposition is clear and easy to follow, even when it lumps up (the start of "Glory" consists of about two pages of description of physics processes, with no characters). But I wish there would have been one or two more. "Luminous" and "Dark Integers" share the same backdrop, and other references tie several other pieces in.
Karen Burnham, in her review at Strange Horizons of this and another Egan collection, sorta concludes that:
"When it comes to Greg Egan, then, it will always be a personal call as to whether you'll grant him the way-far-out-there science and simply enjoy the story, or whether instead not being able to understand the things he's obviously so excited about will ruin it for you. It's important to remember though, that not all his writing is at the top end of the difficulty spectrum. It feels as if there are two Greg Egans: one is so excited about whatever amazing piece of esoteric science he's imagined that he just can't resist writing a story about it. This more famous Egan shows up in Schild's Ladder and Diaspora as well as "Luminous" and "Dark Integers" in the Dark Integers collection, and in "Eugene," and "Into Darkness" in the Axiomatic collection. Then there's the lesser known Egan who uses straightforward extrapolation, usually of biology and computer modeling, to examine "what if" questions of identity and ethics. That realm covers "Ocean" in Dark Integers, almost every other story in Axiomatic, and at least the subtext in most of his novels."
I haven't read enough Egan to say whether I really agree with this (and I found that some of the biological extrapolation in "Oceanic," for example, specially pertaining to post-technological evolution and reproduction, pushed the envelope as much as that concerning matter-as-software etc in "Riding the Crocodile"). But, if Burnham's stance is a useful evaluative strategy, I'm probably guilty of liking the first Egan more. Here's why: there are a million books out there with fantastic characters and marvelous plots and psychological depths. But there are few that tackle, in a manner as consistent and thought-provoking and thoughtful, the more abstract notions that Egan explores. Constructing a story about an idea also harks back to an old SF tradition, and again presents something that no other genre can offer; speculative density. As the future encroaches upon us with ever-greater force, reading this kind of story is no longer simply a cerebral diversion (not to mention that Egan's stories in Dark Integers, even the "type 1" stories, still contain enough characterization, in my opinion, to be not only fun but emotionally engaging). It becomes the exercise of a set of idea-muscles that will prove useful in everyday life.
On the whole, "Riding the Crocodile" was probably my favorite. The ideas are truly mind-stretching, and the writing seems more lyrical than in other pieces. There's also a current of elegiac beauty, part of a greater river of philosophical contemplation on mortality and what gives meaning to our lives, that flows through with subtle power.