WordNet (r) 3.0 (2006):

unappealing
    adj 1: (of characters in literature or drama) tending to evoke
           antipathetic feelings; "all the characters were
           peculiarly unsympathetic" [syn: unsympathetic,
           unappealing, unlikeable, unlikable] [ant:
           appealing, likable, likeable, sympathetic]
    2: not able to attract favorable attention; "they have made the
       place as unappealing as possible"; "was forced to talk to his
       singularly unappealing hostess" [ant: appealing]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "unappealing":
   bitter, disagreeable, dislikable, displeasing, distasteful, sour,
   thankless, ugly, unalluring, unappetizing, unattractive,
   undelectable, undelicious, undesirable, unengaging, unenjoyable,
   uninviting, unlikable, unpalatable, unpleasant, unpleasing,
   unsavory, untasteful, unwelcome