I'm not actually going to finish it. I'm about halfway through (Chapter 21), and I wanted to stick it out, because there are things I like about the book. But I'm enjoying it less and less, and I don't think it's going to redeem itself.
My chief complaint is that the humor is wearing thin. Heller keeps leaning on the same kinds of jokes—twisted, circuitous dialogue that ends in frustration and misunderstanding all around. It's funny at first, but the effectiveness of the technique is more and more sporadic as the story goes on. The narrative structure of the book has a similar gimmick—the story twists and turns through time, wrapping around and through itself repeatedly in an obvious metaphor for the bureaucracy that Heller is sending up. Applied in this broader way it's fine, and doesn't really hurt anything—it might actually work to the benefit of the book, though not greatly so. But on the smaller scale, it gets monotonous.
Nearly as big a problem, though, is the misogyny that permeates the book. Again, this is obviously intentional, and surely it's supposed to reflect poorly on the male characters (as well as probably reflecting poorly on the institution of the army, the situation of war, etc.). But mostly, it's just disgusting. It's no fun to go through, and comes up awfully frequently. Heller's slapstick satire isn't really a robust enough tool to probe this issue in a sustained way. One or two such instances in the book would be poignant. The dozens of them that riddle it, though, strip away any meaning that might briefly have been there.
I'm vacillating between 1 & 2 stars for this book. Because while it has some good writing and interesting aspects, it's overly indulgent in a way that amplifies its weaknesses. If it were a shorter novel, it might work quite well. So in the end, I think it's too simplistic to just give it the lowest rating, and I'm going to go with 2 stars. But I certainly don't recommend reading it.