The Collaborative International Dictionary of English v.0.48:

Unsatisfying \Unsatisfying\
   See satisfying.

WordNet (r) 3.0 (2006):

unsatisfying
    adj 1: not up to expectations; "a disappointing performance from
           one who had seemed so promising" [syn: disappointing,
           dissatisfactory, unsatisfying]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "unsatisfying":
   defective, deficient, disappointing, disheartening, displeasing,
   dissatisfactory, failing, found wanting, imperfect, inadequate,
   incommensurate, incompetent, incomplete, insufficient, lacking,
   not enough, not good enough, too little, unequal to, unfulfilling,
   ungratifying, unqualified, unsatisfactory, unsufficing, wanting