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

cumbersome, cumbrous

WordNet sense 2 (difficult to handle or manage especially because of shape):

awkward, clumsy, ungainly, bunglesome

WordNet sense 3 (difficult to use or handle or manage because of size or weight or shape):

unmanageable

WordNet sense 4 (not practical; not workable or not given to practical matters):

impractical

WordNet sense 5 (lacking grace in movement or posture):

clunky, gawky