I bought this book in preparation for a course on Group Psychotherapy run by a respected counselling organisation which recommended it as pre-course reading matter. It's a big book (nearly 600 pages),and I've only read the first 65 or so, but I've already gained a lot from it.
I'm probably helped in finding it readable by (1)having done an introductory course in counselling; (2) having worked in the office of a counselling organisation. I haven't yet done counselling work myself.
The edition is 2005, so it's not super new; but there's a lot of experience in there, and the cover shows very good reviews.