Even though at first glance they don't seem to have anything in common it's the atmosphere and the overall feel of the romance. In both shows the affections and bickerings between ML and FL are similarly adorable, feverish, loud, heartwarming, sad, joyous, melodramatic, hurtful, amusing, ...
They take you for an emotional ride and you become very invested in the relationships. Also in those of the supporting casts.