This is not an easy read even for mathematicians. But hey, you can't blame the publishers for that ... it's Newton's original text, and it's a work of genius. Newton did use some pretty heavy language and sentence structure, so you have to read it real slowly and multiple times to grasp the concepts.
What I can blame the publishers for, though, is that some of the text is hard to see clearly. Letters and words are cut-off at the margins of the page, so some words are truncated. This makes it even a more difficult text to parse and understand.