All comes down (for me at least, this is something very subjective) to how well it meshes together with the story that's being told, without totally overwhelming it. Being entertaining helps mitigate any issues, and there are some stories where the smugness just rolls off in waves, but that's the main thing; remembering that no matter what message you're trying to offer, the focus has to be the delivery system. It's the difference between (to go to the Grant Morrison well) Flex Mentallo, maybe the single defining text of his career in terms of his relationship with and thoughts on superhero comics, packed with meaning on almost every panel but still an incredibly fun and emotionally charged story all its own, and Arkham Asylum, which is a gorgeous, paper-thin hot mess thrown together for the sake of visual symbolism and half-assed rumination on the nature of madness. To be fair, the latter has its virtues and seems like a genuine effort (the only Morrison comic I'd call truly and utterly pretentious is The Mystery Play), but the message and desire for artistic complexity totally overwhelms the actual narrative. It doesn't have to be subtle--Scott Snyder's Batman work is about as far away from subtle as it can get, but what he's doing meshes well with the stories he's telling, so still works for me--it just has to be kept in mind that first and foremost, a story is being told, rather than a visual essay.