WordNet (r) 3.0 (2006):

unmethodical
    adj 1: not efficient or methodical; "the project failed through
           unmethodical planning"

Moby Thesaurus II by Grady Ward, 1.0:

93 Moby Thesaurus words for "unmethodical":
   aimless, amorphous, broken, capricious, careening, casual, catchy,
   choppy, desultory, deviative, disarticulated, disconnected,
   discontinuous, disjunct, disordered, dispersed, disproportionate,
   eccentric, erratic, fitful, flickering, fluctuating, formless,
   frivolous, gratuitous, guttering, halting, haphazard, herky-jerky,
   heteroclite, hit-or-miss, immethodical, inchoate, incoherent,
   inconstant, indiscriminate, intermittent, intermitting, irregular,
   jerky, lurching, meaningless, misshapen, nonsymmetrical,
   nonsystematic, nonuniform, orderless, patchy, planless,
   promiscuous, rambling, random, rough, scrappy, senseless,
   shapeless, snatchy, spasmatic, spasmic, spasmodic, spastic,
   sporadic, spotty, staggering, straggling, straggly, systemless,
   unarranged, uncertain, unclassified, undirected, unequal, uneven,
   ungraded, unjoined, unmetrical, unordered, unorganized, unregular,
   unrhythmical, unsettled, unsorted, unsteady, unsymmetrical,
   unsystematic, ununiform, vague, variable, veering, wandering,
   wavering, wobbling, wobbly