I adore this book and have read it multiple times, but as with the other Neal Stephenson books I love (Snowcrash and Cryptonomicon), yes, it ends very abruptly—if it can be said to end at all.

The fact that all three books have similarly sudden "endings" makes me think that he just has a very different idea of what an ending really is. It's been a while since I've reread any of them, but I think I'd like to, keeping the notion of traditional narrative and nontraditional ending in mind throughout each just to see if I gain any insight into what he was trying to do... or if I just conclude that he totally gets bored, abandons a book as quickly as possible, and moves on to the next.