What Makes a Song a Worship Song?

Singing praise to God is not a new idea.  I could recount verse after verse in Psalms alone that point us toward praising God in song.  We should be just as eager today to praise the Lord with our voices as David was in his time.  However, that doesn't mean we must sing in the same fashion as David did in order to properly praise God.  Neither does a song need to be slow, melodic or morose in order for us to feel the gravity of the sacrifice that Jesus made for us.  Heck, we don't even know what David's praise music actually sounded like.