I think he was deluded about being the Son of God, but that doesn't mean we should throw out the ethical precepts he advocated. A life lived by the major tenets espoused by Jesus in the Bible - treat other people the way you would want to be treated, be compassionate to people who screw up, take care of people who are less fortunate than yourself - would be a good life. Not surprisingly, those are tenets that are common to most ethical systems, whether they are religious or philosophical.