I am considering becoming a Catholic. A priest told me that I should get a copy of a book called Catholicism, by Fr. Richard McBrien. The book is very expensive, and I was wondering if it is really worth getting.
Don't waste your money. Although Fr. McBrien was once the head of the Catholic Theological Society of America, his views on theology--today at any rate--are way out of line with the Church's official teaching. The book you mention by him is highly erroneous and an unreliable guide to the Church's teachings.
This conclusion was recently announced by an official Church doctrinal review panel here in America, the Secretariat for Doctrine and Pastoral Practices, which studied Catholicism for fifteen years.
Among other things, the book claims that Catholics may, in good conscience, believe that Jesus could have sinned, that Mary may not have given birth as a virgin, and that issues such as women's ordination, homosexuality, and contraception are open for discussion. None of this is true. In fact, the Congregation for the Doctrine of the Faith in Rome recently ruled that the fact women cannot be ordained to the priesthood is an infallibly defined doctrine.
Fr. Augustine DiNoia, executive director of the American secretariat, said the bishops rarely condemn a book, but in this case it was important for them to act publicly because the book is used as an introductory text for Catholics. He explained, "It's like a book review, only it's a book review authorized by the bishops."
Thus, regardless of what some priest may have told you, the bishops have officially declared the book to be an unsound guide to Church teaching and an inappropriate book to use as an introduction to the Catholic faith.
If you would like a truly reliable guide to the Church's teachings, you can get a much less expensive and much more authoritative one in the Catechism of the Catholic Church.