idols is a marketing concept: make people known and even famous with a tv show. The winners first single will sell as a hit... peroid. People buy it because they connect emotionally to the person who has won in 'their' show. That's also why celebs start to sing; they have a bigger chance of selling 'anything' and a musical career is always good for extra attention... and you might earn more...
If people connect emotionally to a song and an artis you can have a hit song, regardsless of the 'quality' of song, production and sound, as long as it is recognised as a song, is understandable, you can sing something along and it sounds ok on avarage sound systems.
Rap is a cultural form of music. Connects emotionally to people with a certain way of life. All the bling bling and flesh appeals to people who are coming from or relating to a poorer 'street' background and of course offenses people who don't understand or relate to that background. Same goes for any style of music really. The music in this case is the spinoff of a lifestyle, the rolemodels of that lifestyle will be most successful, regardless of the 'artistic' value of the song. As long as they are considered hip or hot or excelent by a mass of people who relate to that particular lifestyle.
Certain groups of people like to do the same dance at the same time. It gives them a social satisfaction. Hence the succes of margarena and the likes. Line dancing and ballroom dancing comes to mind.
Some people relate to a certain story. I saw an Oprah show: housewife decides to do something with her own written music, country(?) singer makes it a nr1 hit. Why? The housewife writes in an easy to understand style that connects musically with the emotions a lot of people recognise. The singer (and her team) knows how to translate it to the masses in an easily digestible way.
A hit song should be easy digestible. No worries when you sing about heavy heartbreaking subjects, as long as you wrap it in nice enough to not depress the masses and they can sing along worryless when housekeeping/cardriving/working etc.
A production can make a song instantly recognisable. Bring in the hook. The gimmick that draws attention. People will recognise the song faster, and the ones that like the song will be drawn into it faster. Same goes for sound signature. A sound can work as a logo and make the song stick out.
When speaking about the song material; you cannot define it. Too many different styles, artistic opinions, substyles... Ask two rap-insiders from different areas about their favorite song... probably have a hard time agreeing on a song they both think is great.... just as in any style. Ask people who are not really into rap and they will agree on a great rap song a lot faster...
So as a conclusion to my rambling a hit song probably:
-has parts that are easy to sing along with, lyricly and/or musically
-isn't too style specific/artistic but is recognizable as a style by the masses
-has a hook or specific sound signature
-is brought by an artist people easily relate to, they can love or hate
-is marketed in a way it is heard and recognised by the masses
-has an emotional effect on the masses because of one or more of the above
my two cts of course, ymmv, etc. Just came back from a gig and used this post to relax
cheers
budy