I grew up in Boston and spend every summer there, but am now out in LA.
KLOS L.A. has done the same kind of A to Z twice now, last year over July 4, and just recently over Christmas. When it was over, it was back to the same old boring playlist, but while it lasted, it was great. It took over two weeks to complete, running 24/7. I heard songs I had never heard before, and I've been listening to rock radio since the late 70's.
Listening online to WZLX's A to Z, it sounds a lot shorter. They are already on M, and the songs so far are not producing much of an "oh wow" factor. They're also not doing it overnight, which means being on M after only a few days is not a good sign. Too bad, as I was all geared up to listen to another A to Z. (Plus, their stream is pretty bad quality compared to most.)
What I DO like is the more relaxed feel of WZLX compared to many stations these days. They don't feel the need to have some overly loud promo between every song, and the DJ is talking with a very normal voice. What a relief. The jocks on KLOS sound completely coked, which they probably are, but....
Apparently XM Deep Tracks did an incredible A to Z for years over Christmas, but did not do it this year. I never heard it, but I saw part of the list and it looked really fun. At least 7 versions of All Along the Watchtower, for the person who mentioned that.