I will say that some of the authors include beliefs that might be considered less objective. For example, the Warren G. Harding biography was written by John Dean of Watergate fame. While historians often consider Harding to be one of the worst presidents, Dean tries hard to present him as less of a failure and emphasizes some of his good qualities. I haven't read enough of the other books in the series to see if this is normal.

If you're looking for quick, simple summaries of each President, the American President Series isn't bad. The books are all written by well-respected historians and presented in an easily digestible way. As far as collections go, it's not a bad option. If you're actually looking to learn about the Presidents in depth, you'd be better off looking into individual biographies, such as Chernow's Washington and McCullough's Adams.