WordNet sense 1 (difficult to handle or use especially because of size or weight):

cumbrous

WordNet sense 2 (difficult to use or handle or manage because of size or weight or shape):

unmanageable, unwieldy

WordNet sense 3 (not elegant or graceful in expression):

awkward, clumsy, inapt, inept, ill-chosen

WordNet sense 4 (not appropriate in application; defective):

infelicitous