IMO Cryptonomicon is one of those novels where the journey is the real destination. If you don't enjoy the texture of his prose as it meanders through weird character episodes and technical exposition, there isn't some huge payoff at the end that will make it all worth it. That's pretty much all the book is.
If you're looking for something built around a more traditional plot, Anathem or Reamde might suit you better. People also like Diamond Age, but I think it falls down at the end--IMO at that point he still hadn't figured out how to write endings.
I'm not convinced it's the subject matter and/or length turning people off Cryptonomicon. For all its weird made up words and spec-fic wankery, the fact is that Anathem has a pretty standard YA-esque protagonist and a relatively coherent plot that's paced well (IMO) and carries its momentum through to the end. This makes it read more like a mainstream page-turner than a lot of his other works, the most prominent of which is probably Cryptonomicon. I mentioned Reamde for the same reason, though as you say it's a lot more grounded in the world we know.
It seems like at least one child of my comment agrees with me. It's interesting (and kind of neat) how much fans of Stephenson seem to disagree on the merits of his individual works.
I liked both Cryptonomicon and Anathem once I actually punctured through the wall of frankly gratuitous language, but I fell asleep multiple times on the way. Recommending it to other folks is something I wouldn't do I think, as I don't feel the books were very well written.
I really like all of his novels from Cryptonomicon onwards - apart from Reamde - I did like Fall; or, Dodge in Hell, probably because it wrapped up the Baroque Cycle in such a neat way.
Diamond Age is definitely my favorite, despite the shortcomings at the end. Having said that, "Fall, or Dodge in Hell" is the only book of his that I've struggled to keep reading.
Fall is AFAICR the only one of his that I've at least half regretted reading all the way through, and this from an until recently compulsive -- in the sense that I always finished every book I hadn't given up on already in the first few (tens) of pages -- reader. (Fortunately, I seem to have outgrown that recently.) Anyway, it was weird how bad I found it, given how much I liked the previous Dodge book (especially the part with the kids driving through the "Facebooked" West). [EDIT:] Cribbing from sibling comments: Reamde ? [/EDIT]
In online discussions, I've seen Seveneves getting a lot of flack, which I also found peculiar because IMO it was great; pretty much a return to Snowcrash form but with the added bonus of a few decades experience (so he knows how to write endings etc :-) ).
But after Fall, my second-least-favourite of his may be Diamond Age. Can't recall for sure why, been ages since I read it. [EDIT:] Not that I thought it was bad, I think. Just the least good of many many good books. Apart, that is, from Fall. [/EDIT]
If you're looking for something built around a more traditional plot, Anathem or Reamde might suit you better. People also like Diamond Age, but I think it falls down at the end--IMO at that point he still hadn't figured out how to write endings.