Exactly what it ought to be: a good short overview of Dickinson's life, for anyone who wants to read more than the Wikipedia article about her life but doesn't feel like committing to a full-length biography. The prose is smooth and quiet, with occasional glimmers of humor but no intrusive authorial voice.
Brody keeps interpretation to a minimum, and summarizes existing information rather than contributing original research. He's good at offering context for Dickinson's life and work, and a bit of tentative analysis, but bear in mind he doesn't quote any of her poetry. It's probably safe to assume that anyone reading this book has also read at least a little Dickinson, or what the heck are you doing here?
There are a few grammar errors -- the kind of thing that would slip quietly by a spell check. But we're talking maybe half a dozen total, rather than one or two a page. This is obviously a small independent project, but it doesn't scream "amateur." If those few errors were corrected, this would come across as a thoroughly professional short biography.