WordNet sense 1 (causing or marked by grief or anguish):

heartbreaking, heartrending

WordNet sense 2 (experiencing or marked by or expressing sorrow especially that associated with irreparable loss):

sorrowful

WordNet sense 3 (of great gravity or crucial import; requiring serious thought):

heavy, weighty, grave

WordNet sense 4 (of great significance or value):

important, of import

WordNet sense 5 (shockingly brutal or cruel):

atrocious, flagitious, heinous, monstrous

WordNet sense 6 (morally bad or wrong):

evil

WordNet sense 7 (causing fear or anxiety by threatening great harm):

dangerous, life-threatening, serious, severe

WordNet sense 8 (being in or verging on a state of crisis or emergency):

critical