Here are some quick thoughts on Loraine Boettner's famous book, Roman Catholicism. They are just a few considerations that come to mind about the book.
First, the book is obviously a top seller. You can still buy it new (link) and versions (pirated or not, I do not know) appear for free on the Internet.
Second, this book drives Roman apologists nuts. It's one of the books they love to hate. If they had to name any dead "anti-Catholic" from after 1700, I suspect many would pick Boettner (died 1990). A quick and informal search of the "catholic.com" website turns up hundreds of hits on his name (fewer than the thousands of hits for "James White" or tens of thousands for "Calvin" but far more than a lot of others).
A third consideration is the book's timing. It was first published in the 1960's. Some of the pre-Vatican II issues may not be as useful today as when they were written. For example, the Latin mass is no longer mandatory. Also, Rome has adopted more ecumenical-sounding wordings in many of its documents, which may appear to require some additional explanation (as well as providing room for further rebuttal). Additionally, concern over issues like Communism have waned significantly (though Boettner seems to address Communism rather a lot).
A fourth consideration is the book's documentation. In many cases, it would be nice to have more documentation of Boettner's claims. While I believe that much (perhaps the overwhelming majority) of the book is accurate, it is difficult to verify its accuracy without the aid of footnotes, endnotes, or similar citations. In other cases, a simple typographical error in Boettner can make tracking down his source even more difficult. For example, if he gets the wrong Roman numeral for a pope, it can make tracking down the original for an alleged statement by the pope, quite difficult, to say the least.