These are not absolutes; many books combine writing in more than one of these rhetorical modes (eg The Lord of the Rings begins as a quest and becomes immersive, and I would say even intrusive in the closing section in the Shire; Perdido Street Station is an immersive fantasy into which there is also an intrusion from elsewhere). But Mendlesohn is convincing on the basic point that these are four very different ways of writing the fantastic, which call on writers (and readers) to approach the texts in specific ways. Four long chapters give specific examples for each of the four rhetorical modes; a fifth looks at exceptions to them.
I'm not acquainted with literary theory, and my academic training is in the rather different fields of hard science and history (where the words "polysemic" and "phatic" are not often used), so when I read books like this I am not really looking to participate in the intellectual debate that the author may want to have. I am looking for i) a better understanding of books I have already read and ii) for suggestions of books I might read in the future which may appeal to me, and Rhetorics of Fantasy supplied me with plenty of material on both counts (and I'm brewing a livejournal poll based on my reading of it). It is so far the only book in its Hugo category that I have read, but I'm already pretty certain that it will get my vote.
This is one of two Hugo nominees for Best Related Book available electronically in full from the WorldCon with your membership. (An extract from a third is also provided, which may or may not help as paper copies are not easy to acquire.) I would probably have bought and read it anyway at some point, what with knowing the author and being interested in the subject, but probably not until after the Hugo voting deadline. So the decision to make it available to WorldCon voters has gained a definite Hugo vote and a positive review from me now, as opposed to a possible sale (and a belated positive review) some time in the future. That's probably a good deal.