Imo the most important thing about a trailer is the emotion it brings to the gamer,most of the time this is done with the music or scenes from the game, that emotion can make the trailer way more interesting.
http://www.youtube.com/watch?v=wv3kNPuka4k
Check this out, its in Japan and I can't understand a word of it, but I still really like the trailer, because I played the games when I was a kid and it brought that emotion back to me.








