After reading the flawed but compelling "Against a Dark Background", it was refreshing to read an older work, with a straightforward central premise. In "Cryptozoic", humans have discovered that they can (through the aid of drugs and mental discipline) project their consciousness back to visit the distant past. They can observe but not interact with the past, thus avoiding any number of paradoxes. The main character is an artist, who intends to exploit the past as inspiration to express the spirit of the time-travelling age that is his native time.
I won't give away the ending of the book, but will say that my experience of the climax of the book was somewhat dimmed by my particular copy of the book, which had pages 17-32 printed a second time in place of pages 161-176. I thought at first that the character had backed himself in some kind of time paradox, and was reliving past events with an increased awareness of their real meaning. On closer inspection, it was clear that the text was repeated without variation, and that it was unintentional. I'll have to find a better copy of the book at some point, but honestly, the plot was straightforward enough that it was easy enough to fill in the gaps.
Anyway, this is a good book, but still firmly a part of the older and simpler school of Science Fiction. The novel's central conceit is like a single diamond in a simple setting. Tasteful, easy to appreciate, but not quite as appealing to the jaded palate as a glittering and ornate Ken MacLeod or Iain M. Banks novel.