What a reader makes of “The Mountain Shadow” probably depends on the mood in which she approaches it. A certain generosity of spirit (or at least a good night’s sleep) is required to wade through the pages and pages of cursing, the paragraph upon paragraph of frequently stilted tough-guy dialogue. Roberts’s ambition will seem either admirable, or deeply annoying. On the one hand, he has undeniably created a genuine universe, a teeming underbelly of larger-than-life characters with their misbegotten schemes and drifting lives. On the other hand, Roberts is too transparently determined to write a big book; ambition is also his central ­weakness.

“Teachers, like writers, never die while people still quote them,” Roberts writes near the end of “The Mountain Shadow.” This urge for posterity manifests most noticeably in an effusion of often banal — and, to this reader at least, semi-unintelligible — efforts at aphorism. A few samples are in order. “Time, too, will die, just as we do, when the universe dies, and is born again,” Roberts writes. “Time has a heartbeat, but it isn’t ours, no matter how much of ourselves we sacrifice to it.” Of a woman who is firm in her resolution: “The fall and summit within, what we do, and what we choose to become, are ours alone, as they should be, and must be.” Often, the aphorisms take a transcendental bent, as in the opening sentences of the book: “The source of all things, the luminescence, has more forms than heaven’s stars, sure. And one good thought is all it takes to make it shine.”

The grandiosity of such moments, like eruptions of barroom wisdom from a drunk in the corner, is ultimately overwhelming. Over and over, just when I felt I might get into the story, just as I started identifying with a character, I ran up against one of them. Roberts’s intention seems deadly serious: He is coining a kind of gangster’s Shakespeare, complete with profound meditations on the nature of life, time, ambition, evil, love and everything else that matters. But there is a strange moment about a third of the way into the book that, no doubt inadvertently, captures how absurd and maddening all the aphorizing really is.

Karla and Lin have just been reunited, after two years apart. Almost immediately, they engage in an “aphorism contest,” throwing witticisms and one-liners at each other like hand grenades. What unfolds is a bizarre scene, somewhat unfathomable, almost farcical. “We are the art, that sees us as art,” Lin pontificates to Karla. “Truth is the shovel,” she retorts, “Your mission is the hole.” At one point in this awkward game, Karla accuses Lin of “aphorism har­assment.” It stands as a fitting — if unfortunate — indictment of the book as a whole.