A very good book, designed for engineers desiring to start work with Lucene. Even though it covers an earlier version of Lucene compared to one available today, the principles building search still stand. Personally, I would prefer it to describe Lucene internals in more detail (on track of what's done in chapter 11). The idea of test driven examples is great since it makes it very easy to follow and try out examples.
I liked it, but I wish it'd go a level or two deeper into the actual data-structures. I think that's more due to the 'in action' series than the author's true desires (his blog is a treasure trove on search data-structures and algorithms).
This book has an excellent amount of information pertaining to lucene (from a breadth perspective). However where it fails is in the fact that lucene 9.x.y is significantly different in certain methods and utility than what it was when the book was updated