I read parts of David Lodge, The Art of Fiction (1992) and Wayne C. Booth, The Rhetoric of Fiction (1983) and came up with the chief characteristics of the unreliable narrator:
According to Wayne C. Booth, unreliable narrators are those who convey the gap between what they believe is happening and what the author knows is happening. They do so by means of either being overly ironic, deliberately deceptive or, most often, believing themselves to have information that the author denies them.
In other words (those of David Lodge) their point is to “reveal in an interesting way the gap between appearance and reality, and to show how human beings distort or conceal the latter. This need not be a conscious, or mischievous, intention on their part.” Further: “there must be some possibility of discriminating between truth and falsehood within the imagined world of the novel, as there is in the real world, for the story to engage our interest.”
The implications for my own writing are that I need to think about and explicitly declare both my intentions and those of my narrator before setting down a story in order to be aware of the effect that they have on the story and the reader.
Thinking about the story I am working on now (Imago): the narrator is omniscient in that he knows the thoughts of the three main characters (Michael, Joan and Harry) so straightaway I know that deceit, irony or denial of info to the narrator would be difficult to achieve. My intentions as the author (aside from telling the tale) are to withhold some little pieces of information from the reader (1. that drugs are (and, by implication, Joan is) not responsible for Michael’s state of being and 2. the ultimate fate of Michael) until the end of the story. This deception comes from the author and the narrator is complicit. Therefore the narrator’s intentions are in concordance with the author’s aims and so he/she/it (Do Omniscient Narrators have Gender?) is not, in this case, unreliable.