The problem, I realized, is that Christensen is not particularly good at internal dialogue. She's at her best whenever characters are talking to each other - she's got a real knack for depicting conversations. The characters are vivid, convincing, and thoroughly interesting. But this novel is based around a guy filling a notebook with his musings, and, well, they just get tiresome. Whenever he gets around to talking to someone, it's wonderful, but his long rants about Montaigne, which are meant to be sort of grumpy but ultimately sympathetic, are just dull. The charm of his lasciviousness wears off pretty fast, and while you don't condemn his selfishness, it's not that compelling. The drama of whether or not he'll actually go through with smoking himself to death is gradually replaced by a vague hope that whether or not he dies, he'll quit writing. And really, seeing the world through his eyes grows tiresome. There's a vague, kind of interesting sense that he misperceives certain things, and especially certain people, but you're never really given the chance to learn their side of it, except what you can glean from dialogue, so it doesn't really figure prominently into the overall work.
It's not exactly the problem of how do you create a compelling work with an unsympathetic main character - Hugo is a bit of an asshole, yes, but he's ultimately not such a bad guy - it's more a problem of how do you keep a work interesting if your main character is ultimately a little on the droning side.