Most beat-'em-ups, especially ones that people are likely familiar with and use as a frame of reference, are rather mindless. Final Fight, Streets of Rage, Dynasty Warriors -- these games don't require much in the way of skill or strategy to accomplish a given level or mission. Some people have different ideas of what constitutes a beat-'em-up, though. For some, a game like Devil May Cry or Ninja Gaiden fit the bill.
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"When I was a young man, I had liberty, but I did not see it. I had time, but I did not know it."