Seriously good map: It's mysterious, inventive, subtly off-putting, and occasionally mystifying in all the right ways. Pulls the rug out from under the player once in a while, but never in an overly disruptive way. The progression flirts with being obtuse, too, but digs skillfully avoids falling into that trap. A near-perfect balance of all the elements here, IMO.
Only found 8 secrets on my first run-through (and missed a handful of kills), so I'm sure there's a bit more fun to squeeze out of the map. But it'll likely live long in my Quake memory even if I never revisit this.