I haven't seen a recent edition of this. Mine is about 50 years old, and I'd say the biggest problem is the small pictures. I've heard people complain about their quality, but when you look closely, they aren't that bad. It's just that such tiny pictures were never going to turn out well with the printing resolutions of the day, and probably not even today.Another mini-review to add:
What Birds Is That?, Revised field edition, 1991. Neville W. Cayley
I'm also not a fan of numbered pictures. Is it still like that? having to look them up in the key opposite can lead to mistakes.
Having all the birds on each plate drawn at the same scale can be useful, although it leads to some of them being unnecessarily tiny.