The focus of Gary Thomas's book is on answering the question of the book's subtitle, Why do Christians feel so bad about feeling good?, and his answer seems to be that they don't know how to distinguish between legitimate and illegitimate pleasures from a biblical perspective and tend to feel guilty about pleasures that, from Thomas's understanding of scripture, are sinless and divinely approved. He is also concerned that "neglecting holy pleasure makes us vulnerable to illicit pleasure" (page 197) and defends the concept and experience of holy pleasure, using other adjectives such as good, true, pure, noble, healthy, lasting, etc. to express it. Many will accept his main point. Some, however, may have problems with a few of his personal applications. For example, in Chapter 11 (The Cost of Pleasure), he makes the valid point that "always assuming that 'cheaper is better' doesn't necessarily square with Scripture" (page 173) and uses it to justify occasional splurging on certain (including family) pleasures. He asks: "Remember the repentant prostitute who poured expensive perfume on Jesus, while a few disciples grumbled about the cost, muttering how the money could have helped the poor? Jesus rebuked the disciples, not the prostitute." The context clearly shows that Jesus was more concerned about the woman's salvation than her perfume (which she used to express her repentance), but Thomas uses the story to illustrate that we should "occasionally splurge for the sake of powerful and godly affection" (page 177). If nothing else, Thomas's scriptural references and applications will make one think, even if one may sometimes come to a different interpretation and application.
I recommend Thomas's book for stimulating conversation, even debate, on the topic of the legitimate place and role of pleasure in the Christian's life - and his "Discussion and Reflection" questions at the end of each chapter encourage the benefit of group discussion - but I also recommend comparing his book with others related to the topic. One book Thomas references numerous times is The Power of Pleasure (2007) by Douglas Weiss. He once references John Piper's book, Future Grace (1995), but surprisingly doesn't refer to Piper's influential book, Desiring God: Meditations of a Christian Hedonist (1996 Edition), which some consider to be the definitive biblical exposition on the topics of pleasure and desire from a Christian perspective. Although I'm not a Calvinist like Piper, I recommend reading, even wrestling, with his well-organized text which addresses pleasure and desire in the contexts of the happiness of God, conversion, worship, love, scripture, prayer, money, marriage, missions, and suffering. Piper's tome provides a depth that is lacking in Thomas's text.
In addition to Piper's chapter on money, a good Christian book I recommend reading on the role of biblical finance and giving is E. Jay O-Keefe's Biblical Economics... Beginning at Square One (2006) which is sensitive to the contemporary debate over whether monetary tithing (not giving in general) is a divine mandate for Christians and provides solid biblical principles to use regardless of what side of the debate you're on. He's aware that Christians struggle with coveting and debt regardless of whether they tithe and need to come to terms with the fact that God owns 100% and expects us to give to others as He enables and leads us. Thomas touches on tithing, discussing on pages 80 - 81 "the tithe that is never taught" (in Deuteronomy 14:22, 25 - 26) and even suggests on page 176 that one may have to "skim off a tiny bit of your tithe" to afford a family getaway, although he qualifies it by stating "well, that's between you and God, but in some cases, he might well approve." His coverage of the topic is poor and he doesn't adequately address financial intelligence, inclusive of budgeting and debt management, as it relates to the topic of seeking divinely-approved pleasures.
For the philosophically inclined, if you can get access to a copy of the late Mortimer J. Adler's The Great Ideas: A Lexicon of Western Thought, read the chapters on Pleasure and Pain, Desire, Duty and then the chapter on Good and Evil. These will give you a taste of how such topics were debated throughout history, even by theologians. Good is usually defined as that which is desired for its own sake, but there are real and apparent goods, and when "good" is used as a qualifier, there is also that which is better and the best. Sometimes God wants us to sacrifice certain good things (legitimate pleasures) for what is better, and obeying the personal, dynamic leading of the Holy Spirit is essential to such decision-making. I wish Mr. Thomas gave more emphasis to this. The bottom line is that I recommend his book, but it is not the last word on the topic and one should read other books for a deeper grasp of the subject.