This book was first published at the beginning of the century, and the expected audience was educated Englishman. This means that Trevelyan assumes the reader is already very familiar with not only the general outline of the history but also of the individuals and the roles they play.
For example, to criticize James I he says he "deliberately chose Carr and Villiers." If you nodded knowingly, then you'll probably enjoy the book. But most Americans, unless they have a strong interest in the Stuart monarchy, probably say "Carr? Villiers? Who the heck are they?" Be prepared to say that frequently, and to read at least 20 pages (often more) before the casually thrown out reference is finally explained. If you remember it by the time you get there.
In addition, his writing style nears the heights (or depths) of Victorian impenetrability. Be prepared to reread a sentence a couple of times just to figure out what the subject and verb are, and what phrase modifies which noun. I'm not usually put off by difficult language, but this book went a little too far in that direction even for an individual who reads Dickens and Donne for fun.
Finally, the author's prejudices and opinions are in full display. This book was written before the expectation that an author should remain neutral, or at least not overtly biased, was firmly entrenched. In my opinion, this actually adds to the interest of the book rather than detracts from it, but the reader should keep in mind that the opinions expressed are strictly those of the author and not the unanimous verdict of history.
If you extremely interested in the time of the Stuarts, then you will probably find this book fascinating in its presentation of the historical judgement of 100 years ago. If you are not already well informed on the subject and not a fan of complex language where plain would do, then you'll be better off looking elsewhere.