Good games don't even need difficulty settings, if their gameplay's depth includes enough to make everyone play at their own level of skill and still find a satisfying challenge.
I especially think about good arcade games. Masterpieces like Ikaruga or Crazy Taxi, which you can play superficially, or more deeply to reach the real challenge.
Even when you're not a highly skilled player, you have fun.
If you're a badass warrior from hell™, you still have fun.