What matters far more is the intensity of sensation, whether it’s excitement or pain or contentment. And it’s not the overall average of the experience that people remember, but how they felt at the most intense moments, combined with how they felt right as the experience ended. Psychologists call this the “peak-end rule.

— Drake Bennett (2010) The Best Vacation Ever

In synthesis, I can extract from the article those points:

1. Intensity: what matters is the intensity of the sensation
2. Peak-end rule: the intensity peak is in relation to the intensity at the end
3. Short duration: more days doesn’t mean more enjoyment
4. Breaks: stopping the sensation and then resuming increases its perception
5. Variation: enjoyment also stems from avoiding routine and doing novel things

The article gives also some hints to researches that showed the validity of these results if you’re interested in.