Though “Watchman” is being published for the first time now, it was essentially an early version of “Mockingbird.” According to news accounts, “Watchman” was submitted to publishers in the summer of 1957; after her editor asked for a rewrite focusing on Scout’s girlhood two decades earlier, Ms. Lee spent some two years reworking the story, which became “Mockingbird.”So, although it is set ahead of the first book, it's a bit like a first draft of the famous one.
I wonder how many people ordered the book on the basis that it was a sequel written after the first? Because coming to the book on the basis of how it was really written may well lower ridiculously high expectations.
The Guardian did have a lovely graphic/audio accompaniment to the first chapter, though. (Actually, I don't care for the audio. It quickly becomes tedious.)