For the most part, the narrative tone reflects Robert Jordan's own temperament, which makes sense, given how much of the narration is bound up with his own thoughts. He's a pretty chill guy, really chill, in fact. His goal is to get the job done, and he's left much more nonplussed by things than the average human being would be. For example, when Anselmo, Jordan's best friend, dies, we get the following: "Anselmo lay face down behind the marking stone […] He did not turn him over to see what the piece of steel had done. He was dead and that was all" (43.127).
Talk about not overreacting. Robert Jordan (or maybe Ernest Hemingway?) also thinks of himself as pretty worldly wise and street smart. In many of his "worldly" descriptions, especially of the "essence" of Spain, politics, and whatnot, he speaks as if he were the unchallenged authority who knows from real, down and dirty experience.
Knowing the ways of the world usually means knowing how corrupt and disappointing reality can be in contrast to any idealized pictures of it, so, yes, there's a fair amount of cynicism, often cuttingly humorous. This sometimes leads the great authority to second-guess himself, especially if he's getting too emotional or excited: "There's no one thing that's true. It's all true. The way the planes are beautiful whether they are ours or theirs. The hell they are, he thought."
Oh, and that's the last bit. Every so often Robert Jordan does get really excited (it's part of his on-going awakening to start getting affected by things), and then no one knows what's going to happen. Well, actually, we have a pretty good idea. But check out "Writing Style" for that.