In my mind, I picture Pynchon reading Cryptonomicon and thinking to himself, "He's doing me, only more sprawling and diffuse. Oh yeah?! I can do that squared. Instead of WWII, I'll do it before and after WWI (with only the barest mentions of the war itself). Instead of 918 pages, I'll do 1,085 pages. Instead of cryptography, I'll do quaternions."
It's a big honking disconnected mess, interspersed with flashes of genius.
One Lovecraftian interlude involves a fictionalized analogue of the recovery of Ahnighito, a slumbering and inimical god of the Inuit, awoken by its travel to New York City.
It would almost be enough to give up on Pynchon, except that Inherent Vice is set in Los Angeles, and is a mere 369 pages.