The Collaborative International Dictionary of English v.0.48:

Unfavorable \Un*fa"vor*a*ble\, a.
   Not favorable; not propitious; adverse; contrary;
   discouraging. -- Un*fa"vor*a*ble*ness, n. --
   Un*fa"vor*a*bly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unfavorably
    adv 1: showing disapproval; in a disparaging way; "he reviewed
           the play unfavorably" [syn: unfavorably,
           unfavourably] [ant: favorably, favourably]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "unfavorably":
   afield, amiss, askance, askant, astray, awry, badly, captiously,
   censoriously, conflictingly, contrarily, critically, detrimentally,
   disapprovingly, inauspiciously, opposingly, oppositely,
   reproachfully, unfortunately, unluckily, unpromisingly,
   unpropitiously, untowardly, wrong