I was worried that his introductory grammar would be written so that the language was inaccessible for undergraduates. I expected something similar to his extraordinary grammar, A Coptic Grammar, a book not for the linguistically-challenged!
Not only are my worries set aside, but I have decided to embrace Coptic in 20 Lessons and use it this fall as my introductory grammar instead of Lambdin, even though this does mean that I will have to work through all the vocabulary and exercises anew, and replace my old ways of talking about grammatical points with Layton's verbage.
The grammar is laid out well with complete paradigms in each lesson. The exercises (once you get going) are taken from the literature (yeah!), so no nonsense sentences to deal with. And the best part of the book is that all those little things that you encounter and try to figure out once you start reading, are explained by Layton as he goes. So he talks about things like reading from a manuscript and scribal practices - where superlinear strokes are placed, when scribes don't write certain letters, and so forth. So the book is a nice combination between seasoned information and beginning grammar.
It looks like students will only be able to get through one chapter a week though. So if you are used to getting through Lambdin's grammar in a semester, I don't think that is going to happen with Layton's grammar, unless there are a few chapters that can be doubled up in a week. The last part of the book contains three chapters from Coptic Mark. Layton suggests that students can finish the grammar and read the entire Gospel of Mark in two semesters.
So here I go, changing my book order, and hoping I don't live to regret it!