This is simply a magnificant work! This contains the complete Hebrew text of Genesis, the JPS's new English translation, and an extensive original commentary that illuminates the text like a 1000 watt searchlight. On average, each four or five lines of text gets a full page of explanation and commentary, so every subject gets covered in detail.
Sarna, like all the JPS Torah commentators, makes use of traditional rabbinic commentaries, and the Mishna, Midrash and Talmud. But it doesn't end here: The commentary goes on to make good use of literary analysis and comparative Semitics; intertextual commentary relating each book to other biblical books, and evidence from modern archaeological, discoveries.
It manages to be respectful, religious, and authentic to the Jewish tradition, while at the same time rigorously adhering to the highest standards of biblical criticism and intellectual honesty.