(Warning: spoilers!)
I finally finished the beast. I made my first attempt a few years ago, and because I'm a relatively slow reader, it took me months to get within 100 pages of finishing it... before I gave up. This time I did it, in seven months. I've only read one other Pynchon book, Vineland, and I found it relatively easy to read and entertaining. And I'd heard a lot of good things about Gravity's Rainbow so I thought I should try it, but my memory of my last attempt was that 20 or more pages in a row would be pure genius, followed by 50 pages where I had to slog through, paragraph by paragraph, in a war of attrition. I was mostly right.
That first page was really hard. I kept thinking, "Is this a dream?" No, I guess not. Where is he? Huh? No wait, it is a dream! But then the banana breakfast sequence rewarded me for persevering.
Characters were still being introduced for the first 100 pages, but it works because each new character (or pair of characters) is introduced through a mini-chapter on what they're up to here in 1941 London. Then we move on to a character somehow related to the last, in a loose chain that's kind of like a "six degrees of separation" game.
I have to admit, it was really rough going at the end. When I got to page 700, which is apparently about the place I gave up last time, I knew I was gonna be in for a tough climb. The plot completely dissolves. At least one major character (Slothrop) and one minor (Jamf) are declared to have never existed. The free-wheeling stoner rants take center stage but not many of them last more than one page before Pynchon gets distracted and switches to another topic.
I was mentally prepared to be let down, to have no closure or conclusion, so I wasn't mortally disappointed like I was at the end of Cryptonomicon or Infinite Jest, but I was also a little bit taken aback. There is a conclusion to one of the plots: We find out what Imipolex G is (turns out to be an extended sex joke), and what was actually in the final 00000 rocket. Although, if you didn't know what was in the 00000 rocket by the time it's revealed, you haven't really been paying attention, since Pynchon drops hints every 20 pages like a giggling schoolgirl who can't keep a secret.
Disappointment aside, the book overall is worthwhile, but more as a collection of stories. There is absolutely no point in obsessing about getting to the end and hoping that any of the loose ends will be tied up. (I wish I could take a time machine and go back and tell myself that.) It's more of a huge rambling snapshot of a few months in the lives of a dozen really interesting characters. The best sections stand on their own as awesome short stories without requiring any context: Roger & Jessica's spontaneous church visit, Pökler's backstory and the German "Dozen Children" themepark town, the party boat on the Oder, the balloon ride across the Zone, the squid attack, the party in France with the tank, etc.
There's something I think Pynchon is trying to do over and over here: drift off into some free-association riffing, away from the story, and start dropping freeform stream-of-consciousness babbling that, when it works, becomes kind of transcendant and magical. I actually bookmarked the pages where he hit the mark with one of these because they're really incredible. There was a really great one when Roger & Jessica made a spontaneous stop at a church for holiday services and Jessica's mind drifted off to thoughts of a giant room filled with empty toothpaste tubes waiting to be recycled into useful metal for the war effort. Sadly he didn't edit out many of the ones that didn't work, so sometimes it comes across as trying too hard.
On the other hand, he's not a math & science guy. The descriptions of Roger's statistics work are best skimmed with your brain turned off, and Pointsman's Pavlovian experiments seem like they exist only to show that's he a cruel man. Unless we're supposed to think that he really believes that mindlessly repeating someone else's experiments over and over is a sure way to win a Nobel prize.
I think I'll feel better about the book after it's had time to sit in my brain for a bit (I just finished it last night). But it's definitely time to move on to more light reading after this.