There are a few things to know about this book.
First, it is a coffee table book more than it is a practical manual of "mixology". This is evident from the beautiful photos and the fact that more attention is paid to style than to substance. In part, this is probably due to the fact that most people are more familiar with absinthe as a stylish drink than they are as a viable spirit.
Second, absinthe is still a little faddish. This goes with the first. Realistically, if you tell people that absinthe is your favorite spirit, they're likely to think that you're either a poser or that you're a lush. In reality, the complex flavors of absinthe mean that (for those inclined to spend money) it is as reasonable a drink to enjoy amongst company as a fine Scotch. While I have tried a few of these cocktails, I vastly prefer absinthe mixed with something simpler, like Tarhun (a tarragon-flavored soda) or with water. I roll simple, but deep.
With those things in mind, it's not really that surprising that I don't really think that actually MAKING the cocktails is the point. Rather, you are supposed to put this book somewhere obvious (preferably near your absinthe glass and spoon), and have people marvel at your worldliness. Then, when they suggest a recipe to try it out, you mention that you're just fresh out of a few of the ingredients. In this way, your bluff isn't called.
If you ARE forced to actually make some of these cocktails, though, there are two things to keep in mind.
First, many of the ingredients in the book are relatively expensive. If you are willing to drop a significant amount of money, you can try most of the recipes. Many of the liquers required were things that I have never even heard of. Most of them were things that I've never tried. Be prepared to use a lot of things only once, and be prepared to spend. As such, you should perambulate and dodge it as long as possible.
Second, due to the obscure nature of absinthe, most of the cocktails don't really USE absinthe. They involve glass rinses, and a few drops of absinthe. Does that get the flavor in there? Probably a little. But often times, unless you're drinking top shelf, the delicate flavors of absinthe are not going to come through. You might as well just grate a little fennel into your rye and call it good. And if you're dropping stacks on top shelf for every ingredient, well...I guess that you have the dime to spare to buy this just for satisfying your curiosity. But, if you are avoiding making these, as I have suggested
As a reward, though, if you do have to mix one of these, the recipes are generally very interesting sounding, they usually look beautiful and have luscious, exotic names (like Necromancy or Sazerac), and the few I've tried are pretty decent. That said, as Eric C. Sedensky said, substitutions would have been welcome. But, it is important to recognize that this is not really a recipe book so much as it is to showcase the purchaser's sophisticated palate and interest in the forbidden, so I can't over-fault the author for providing a book that Asmoranomardicadaistinaculdacar would be proud of.
(Finally, I am taking a star away from this for the recipes that say, "Coat the glass with absinthe and discard the excess." Never discard absinthe. Ever.)