WordNet (r) 3.0 (2006):

overcritical
    adj 1: inclined to judge too severely; "hypercritical of
           colloquial speech"; "the overcritical teacher can
           discourage originality" [syn: hypercritical,
           overcritical]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "overcritical":
   captious, carping, caviling, cavilling, censorious, critic,
   critical, cynical, demanding, difficult, exacting, fastidious,
   faultfinding, finicky, fussy, hair-splitting, hairsplitting, harsh,
   hypercritical, hypersensitive, morbidly sensitive, nagging,
   niggling, nit-picking, overconscientious, overfastidious,
   overmeticulous, overnice, overparticular, overprecise, overrefined,
   overscrupulous, oversensitive, oversqueamish, pettifogging,
   picayune, picky, querulous, quibbling, severe, small, small-minded,
   trichoschistic, ultracritical