adjective satellite (s)

• requiring full use of your abilities or resources(adj.all)

  Example:
  Performed the most challenging task without a mistake.
  

  Synonym:
  ambitious
  

  source: wordnet30
• stimulating interest or thought(adj.all)

  Example:
  A challenging hypothesis.
  

  Synonym:
  thought-provoking
  

  source: wordnet30
• disturbingly provocative(adj.all)

  Synonym:
  intriguing
  

  source: wordnet30