So, not really a gameplay question, but, we all know the default music sucks. Mandolins are nice, but after the first five minutes, well...
It most certainly does not suck! Sure, I wouldn't listen to it (or anything) for more than a few minutes (unless I'm listen analytically), but it's quite an interesting piece. Also it's not mandolins. It's one acoustic guitar.
But I usually turn on a Pandora station. Usually a rock station (with the likes of Stone Temple Pilots, Muse, Green Day, Metric, the Beatles, Foo Fighters, Nirvana), sometimes jazz (Gimme some Miles Davis or Dizzie Gillespie) or classical (woo Brahms) or broadway. Sometimes I'll listen to Super Nintendo soundtracks.