Although I
cannot comment on "principles of economics theory" by Snyder/Nicholson, I just took Intermediate Microeconomics using their Intermediate book and it was horrible. In many cases concepts were oversimplfied, worded terribly and offered little to no examples of how to do end-of-chapter problems or test problems, which was especially problematic in my case because my prof. was equally terrible at explaining how to do problems. After finishing the course I went and bought an old copy of the Intermediate Micro book by varian and it is far supurior but very math intensive.
For Intro Micro, our prof. used the book by Frank/Bernanke and I found it to be excellent in explaining concepts clearly and completely. We used the newest version of this: (
amazon)