Synonyms for Critical:

adj.

critical (adjective)
finicky, derogatory, Fault-finding, pedantic, judgmental, caviling, harsh, disparaging, carping, picky, captious.
dangerous (adjective)
perilous, hazardous, risky.
discriminating (adjective)
discerning.
fastidious (adjective)
finicky, accurate, conscientious, perspicacious, prudish, squeamish, discerning, priggish, literal, delicate, flawless, fussy, demanding, careful, picky, punctilious, hypercritical, persnickety, mincing, diligent, Qualmish, prim, meticulous, epicurean, correct, methodical, exacting, rigorous, severe, fastidious, discriminating, dainty, choosy, scrupulous, proper, particular, precise.
fault-finding, detracting (adjective)
satirical, penetrating, hypercritical, carping, derogatory, overcritical, disparaging, discerning, caviling, cutting, analytical, captious, severe, sarcastic, fussy, exacting, demanding, withering, biting, finicky, reproachful, censorious, trenchant, sharp, discriminating, nagging, scolding, particular, cynical, hairsplitting.
important (adjective)
high-powered, influential, consequential, central, serious, heavyweight, salient, important, eminent, considerable, world-shaking, major, distinguished, earthshaking, grave, pivotal, meaningful, big-name, momentous, prominent, noteworthy, crucial, big-wig, notable.
intelligent (adjective)
penetrating.
life-and-death (adjective)
earthshaking.
severe (adjective)
draconian, stern, crisp, puritanical, fundamental, demanding, obstinate, ascetic, acute, gruff, keen, precise, spare, dour, intense, cutting, blunt, chilly, strict, raw, rigid, frosty, rigorous, spartan, disciplined, inflexible, grim, stark, bleak, imperial, sharp, censorious, caustic, harsh, oppressive, acrimonious, dry, acerbic, short, meticulous, intolerant, curt, lean, brusque, correct, tart, stiff-necked, abrupt, hidebound, severe, astringent, prudish, basic, brisk, uncompromising, relentless, austere, piquant, exacting, authoritarian, stringent, strait-laced, obdurate, icy, cool, unbending.
sharp (adjective)
sharp.
urgently important (adjective)
consequential, dangerous, decisive, hazardous, risky, desperate, crucial, climacteric, perilous, acute, pivotal, serious, grave, vital, deciding, significant, momentous, dire.

n.

conceptual, explanatory, judging, observant, popular, judicious, deterministic, analytical, penetrating, abstract, perceptive, theoretical, nonconformist, utopian, interpretive, trenchant, orthodox, metaphysical. acid, ad hominem, biting, flattering, sarcastic, blistering, acrid, accusing, nagging, accusatory, reproachful, satirical, faultfinding, withering, barbed, scolding, hairsplitting, cynical. intellectual, thoughtful, deductive, insightful, smart, praise, reasoned, incisive, meditative, sound. unwell, ill, unhealthy, unfit, sick, frail, value, infectious, fragile, worse, failing. impossible, trying, awkward, difficult, testing, intractable, safety, climacteric, intolerable, thorny. critical (noun)
captious, deprecative, dire, dangerous, quibbling, evaluative, vital, overcritical, pettifogging, decisive, grave, vituperative, carping, severe, judicial, scathing, discriminative, indispensable, appraising, caviling, serious, supercritical, hypercritical, acute, censorious, desperate, grievous, nitpicking.
crucial (noun)
deciding, significant.

Other synonyms:

intolerable, faultfinding, reproachful. intractable, trenchant, thorny, impossible, testing. decisive
decisive.
expository
explanatory.

Usage examples for critical

  1. In Moore's case, however, the present moment seemed critical – The Mysterious Rider by Zane Grey
  2. I have scarcely time, my dear fellow, and then my critical opinion will not fill enough space either. – Bohemians of the Latin Quarter by Henry Murger