After just completing my first reading of Ulysses, I am joining my voice to the GR chorus of appreciation for Blamires's guide. MJ referred to it as indispensable in his review, and I concur with his assessment.
Blamires provides short, beautifully written overviews of each episode, but these overviews are not simply summaries (although his summaries are indispensable in certain passages and episodes that otherwise could be difficult to follow). Instead, Blamires also discusses some approaches to interpreting Ulysses, indicating themes and motifs that reappear throughout the novel, providing some gentle guidance for the reader to begin appreciating the intricate connections that Joyce weaves throughout the novel.
I have described Blamires's The New Bloomsday Book as serving a function similar to that of synopses of operas in playbills. He provides a sense of the action and some important elements to consider when reading Ulysses, but he does so in such a way that readers remain free to respond to Ulysses on their own terms. It's a very difficult balancing act, and one that he executes perfectly.