I have the three-volume slipcase edition, and that
really helps with the endurance-test aspect of things (I know that it's technically split into three books whatever version you buy, but there's a not-inconsiderable psychological boon in seeing and holding those seperate volumes and thinking 'I can probably manage this one.') I also read a different book in between each volume of Jerusalem, just for a bit of lighter fare to help break things up, and give me time to mull and ingest what I'd read.
All of which I suppose is set-up to say - it
really clicks together, I think, with that second volume, Mansoul. The Boroughs was incredible, but I was a good 150 (dense) pages in before any sense whatsoever emerged of a linking hand guiding it all (
specifically the bit where you read the Freddy Allen/Peter the monk meeting, but this time from Peter's point of view). Individual chapters were incredible, but that nagging 'Where the hell is this going?' held my enjoyment back slightly. In Mansoul, however, you've got Moore laying out his whole cosmology - Heaven, Hell, Life, Death, Time - and it's just stunning stuff. Probably the best of the three volumes.