The Collaborative International Dictionary of English v.0.48:

Characterless \Char"ac*ter*less\, a.
   Destitute of any distinguishing quality; without character or
   force.
   [1913 Webster]

WordNet (r) 3.0 (2006):

characterless
    adj 1: lacking distinct or individual characteristics; dull and
           uninteresting; "women dressed in nondescript clothes"; "a
           nondescript novel" [syn: characterless, nondescript]

Moby Thesaurus II by Grady Ward, 1.0:

109 Moby Thesaurus words for "characterless":
   amorphic, amorphous, anarchic, arid, baggy, bare, barren, blah,
   bland, blank, bleached, blobby, bloodless, blurred, blurry,
   chaotic, childish, clear, cold, colorless, confused, dead, devoid,
   dismal, disorderly, draggy, drearisome, dreary, dry, dryasdust,
   dull, dusty, effete, elephantine, empty, etiolated, fade,
   featureless, flat, formless, futile, fuzzy, hazy, heavy, ho-hum,
   hollow, impotent, inane, inchoate, indecisive, indefinite,
   indeterminate, inexcitable, infantile, inform, insipid, jejune,
   kaleidoscopic, leaden, lifeless, low-spirited, lumpen, misty,
   namby-pamby, nondescript, null, null and void, obscure, orderless,
   pale, pallid, pantywaist, pedestrian, plodding, pointless, poky,
   ponderous, powerless, shapeless, sissified, sissy, slow, solemn,
   spiritless, sterile, stiff, stodgy, stuffy, superficial, tasteless,
   tedious, unclear, undefined, unlively, unmanly, unordered,
   unorganized, unrelieved, vacant, vacuous, vague, vapid, void, weak,
   white, wishy-washy, with nothing inside, without content, wooden