Clocking in at 170 pages, this is a good, quick, overview of the history of Catholics in America. The author relates this history mainly by focusing on important Catholic persons who shaped Catholicism in this country, before and after it was a country, and telling their stories. Sidebars cover a variety of topics but usually can be skipped without fear of missing anything.
Decently balanced, the author does tend to focus a bit more on the progressive aspects of American Catholicism, particularly once it is well established later in the 19th century. The immigrant theme of the book, from the title, is an indicator that social justice is an important focus of this work.
If you have started here, move on to other more comprehensive titles. If you have not read this book yet, but have an interest in American Catholic history, no harm reading this but don't stop here.