Lewis's trilemma (liar, lunatic, or Lord) misses a lot of more plausible options.
Misrepresented: We don't have a single word written by Jesus directly, and our only sources are second- or third-hand sources written roughly one generation later. With a devout cult springing up in his wake, it's not that far-fetched to see a tale growing in the telling, until we've got Jesus proclaiming his divinity from the rooftops in the gospel of John, roughly 70 years later. (Contrast this with the gospel of Mark, where Jesus constantly admonishes people not to give away his "secret identity", so to speak.)
Misunderstood: Being the messiah had a specific meaning in the cultural context that Jesus preached in, and "god incarnate come to earth to sacrifice himself to himself" was not it. So, even if Jesus believed that he was the messiah, and went around telling people thus, this does not necessarily mean he (and others) understood it the way Christians do.
Myth: While it's unlikely that there wasn't a historical Jesus, it *is* possible that virtually nothing factual about him is left in the account we find in the new testament.