Maybe you like more mature male leads (I do too). In ep 1-3 they really emphasise the playboy immature aspect of the Prince. Note - he's the crown prince, not the king as all the subtitles say. He rules nothing, he doesn't want to rule and his playboy ways are deliberate because he doesn't want to be king. All this is so that when he matures later on, you will see the development and the truly great backbone that he has. Also, this drama is carried by the characterizations of Eun Shi Kyung and Kim Hang Ah. Those characters are the pillars by which the prince matures later.
If you want specific spoilers, drop me a line. :)