There are a number of things that can help to make a song more memorable and perhaps more likeable. These include having a fairly basic repeating rhythm, with occasional variations, a melody that is almost predictable, but every so often takes you by surprise, lyrics that are from the heart, a chorus that is memorable and catchy, musicians and vocalist who are putting their soul into the recording, not just reading it straight from the page, production that is good, not formulaic. This is by no means an exhaustive list, there are plenty of great songs that use just a guitar, but the words take on special meaning (Bob Dylan for instance). Classical music tends to use repeating themes with variations in the melody, jazz uses improvisation, rock uses blinding guitar solos and the vocals as an instrument. Take your pick!