I think a song becomes interesting when the singer not only sings a melody but also knows how to interprete the lyrics and tell the story. 

Pronunciation is very important. First of all because it makes you understandable. Second, because we sing on vowels, not on the consonants. The better you pronounce while singing, the easier it becomes. It is jut a matter opening your mouth on all the vowel so that the breath can flow. This way the voice gets the opportunity to sound freely. Singing is a combination of breath, posture, pronunciation and interpretation. And obviously: fun!