I didn't find the beginning quite a slog but I did wonder if there was going to be a "plot" in the conventional sense. As you say, the rest of the book was a near-continuous crescendo. One scene in particular (Saunt Bucker's Basket!) made me literally stop reading while my brain processed.

My wife read my copy after me. If I remember correctly, she more or less read up to that scene in 5-10 page increments, and then read from that scene to the end in most of one night.