The copy I have of this, from the library is from 1980 and is described as a “Preliminary Edition.” A quick look at Amazon tells me that there is a 2nd Revised edition from 1992 though I can’t comment on what changes were made.
Originally written for Summer Greek Intensives in New York, the text certainly lives up to the “Intensive” in the title, trying to deliver 2 years of college level material over 11 weeks (six weeks to cover all the grammar, 5 weeks spent reading Plato and Homer: the book only covers the grammar).
The structure of the material is unrelenting grammatical information, in a classic instructional style (no inductive learning here), with each unit followed by grammatical drills of the Grammar-Translation method: translation, parsing, morphological manipulation, grammatical analysis.
Admittedly I have never used H&Q as a teaching text, nor have I put myself through all its rigours. It does make a handy volume to go through and make one’s own grammatical notes, because the grammar is laid out very clearly through units and numbered sections, and the contents page tells you where to find everything. This is very pleasing to see (if you’re going to have a grammar-based approach, a really clear contents is critical, in some ways more important than a good index).
Would I recommend it? No. It’s like Wheelock’s Latin, but less forgiving.
That said, if you want an old-school, master-all-the-forms approach, H&Q is attractive if only because they lay it out so well. The text lacks up-to-date linguistics, but the exercises are also a smorgasbord of traditionalist training, if that’s what you’re after.
The acknowledgments for the 1992 edition mention only “a few corrections and improvements” without going into greater detail.
I learned Greek via this tome, and I am afraid it was not particularly enjoyable. While it is extremely comprehensive and we did take a year and a bit to cover the entire book, its thoroughness was also overwhelming. As a language learner, I much prefer having things broken into smaller chunks that I can master before adding another chunk. Each chapter in H&Q covered so much and if I recall correctly, you couldn’t do the exercises without having covered the whole chapter. Sadly, I loaned my copy out a year or so ago and never got it back.