Linguistics is supposed to be vague and boring. And believe me, in 99% of the time it is both, the latter stemming inevitably from the former. Larry Trask, however, is one of those few amazing authors who succeed in presenting linguistics in a manageable form, thus revealing its fascinating nature, which is usually hidden under heaps of elaborate, sophisticated, why-say-it-simple-if-you-can-say-it-complicated phrases.
“Historical Linguistics” is student-oriented. While writing many linguists tend to forget that their textbooks will be read by students who might have little or no experience in the given field. Many of the writers go further and forget the simplest rules about acceptability of the text and information load. Let’s not mention any names. Trask's “Historical Linguistics” escapes all these traps with ease and is a pleasure to read. I laughed out loud more than a few times and that says a lot about a textbook. The feeling is more one of having a conversation with a teacher, rather than reading.
At the same time one shouldn't be left with the impression that the textbook simplifies the matter, because this is not the case. It has its share of terminology and it counts on the reader's knowledge on other branches on linguistics, mainly phonology, morphology and syntax. It is not suitable for people who are new to linguistic theory.
I strongly recommend the Trask’s “Historical Linguistics” to all students in the field.