I think dynamics are indeed a very large part of it - in spite of being the same for such a long time, Velvet Revolver's Heroin doesn't particularly bore me, for instance. Sometimes I can't listen to it because it doesn't go with my current mood, but it's not like it just fades into the background. That isn't the case with Ryoshima Plains: I even went ahead and listened to it three times before Theme of the Last Time Travel (which I had been listening to lately for reasons unrelated to the contest), just to be fair and...nope, no dice.
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Currently playing: League of Legends, Chrono Cross.
Current Projects: Fool's Overture, CYOA: http://www.gamefaqs.com/boards/8-gamefaqs-contests/60143513