In Your Dreams is a funny book. Make no mistake about that. It blends a lot of every day life together with magic for laughs and has a lot of Pratchett/Adams style humour from taking things to their logical extreme. The language is good throughout with laugh out loud imagery and good use of hyperbole. Outside of humour the writing style is just solid in general, scenes and settings are well drawn.
With that in mind, the book has some problems. If you enjoyed the first book in the series (The Portable Door), or are a fan of Holt's work in general, you probably won't mind anything I have to mention below. Also, I'll say now, I wouldn't worry too much about this being the middle part of a three parter. I'll get to why in a minute...
The main shortcoming of the book is its characters. Or rather, its heroes. The villains and side characters of the book are exceedingly well drawn, from the lusty goblin receptionist to the main character's talking German car, to the Queen of the Fey, count Judy. These characters and more are well done and very enjoyable to read.
The problem is our hero: Paul Carpenter. Like most Holt protagonists he is a very generic, gormless milquetoast hero. Initially his cluelessness is a kind of attractive quality, as we, the reader, can identify. But as the book(s) go on, it becomes more and more annoying that Paul never has a clue about anything, and never has the confidence or the good sense to just ask people when he's out of his depth. He has no particularly notable or interesting character traits and this is so painfully obvious when he's standing opposite other characters who are better fleshed out. It's not impossible to get away with a somewhat generic main character, but they need just a little bit more. Arthur Dent is how to do it right, Paul Carpenter is how to do it wrong.
This goes doubly so for the heroine or love interest, Sophie. Sophie spends about 80% of the book off screen, and many characters comment repeatedly on the fact that she's a cold nasty young woman who isn't particularly nice to anyone. Yet when she shows up and... is cold and nasty and not particularly nice to the love of her life, Paul, we're still expected to route for Paul as he dives head over heels in love with her. I can kind of get behind Paul a tiny bit because he's the point of view character, but I can't even remotely begin to understand why we're supposed to like Sophie.
Beyond that, the book has a couple of other problems; plot points or important magical macguffins are occasionally introduced mere moments before they become very important, some plot twists don't exactly make sense if you stop to think about them, and there's at least one character who disappears in the final act never to be seen again. While there are good reasons for her disappearing, nobody comments on it.
Since there's no character arc worth speaking about and the major plot arc of the trilogy is pretty obvious, I think it's safe to dip in on this, the second book, if you want to, rather than starting on Portable Door.
Like I said at the start, it's very funny, and a lot of the characters are great. I'd just caution avid readers that if they want a hero who oozes personality, look elsewhere.