First off, the content is terrific. It's the definitive story of Wallace's time in Indonesia. There is a lot of fascinating material, about the science, the culture, and the view of those things from the perspective of an English scientist. Much of it is just riveting, but some parts drag a bit.
In many ways, I found the descriptions of the process more interesting than the descriptions of the items and specimens he collected. Late in the book, the descriptions of sailing small boats through difficult waters are quite compelling, as are descriptions of the process of collecting itself. (For example, he really wanted to learn about orangutans in Borneo, so they went out and shot a bunch of them.)
A couple of editorial comments about the narrative thread are needed:
Wallace arranges the material geographically, not temporally. That is, he takes the islands and regions more-or-less West-to-East, which is *not* the order in which he visited them. As such, the narrative flow is quite odd at times, causing him to refer back and forward in the text, and also requiring him to repeat some material.
I should also mention that Wallace often refers to plants and animals only by their "scientific" names, sometimes because he's discussing the classifications, but often just because. That really interrupts the flow for a reader unfamiliar with the names. I didn't have a problem with it, but sometimes the lists do go on a bit.
Now, some comments about this particular edition:
1. It appears to be a reprint of a previous edition. Instead of resetting the text in a newer typeface and format (with corrections and such), it's just a reprint. That might not be too back, except for the fact that the typeface is Very Small, making it a bit difficult to read. The material is dense enough; it would be helpful to have a clearer, easier-to-read printing of the text.
2. Compounding that matter is the fact that the pages have HUGE margins. There is at least an inch of space wasted (blank) on the side and bottom of each page. That makes the book much bigger and heavier than it needs to be. If they wanted bigger pages, they could at least have printed the text bigger to take advantage.
I guess if you want to take copious notes in the margins, this might be great for you. Otherwise, I would look for another edition that isn't both wasteful and hard-to-read.
It's still absolutely worth reading, but I would look around for a different edition if I were shopping again.