nice sub-panel, but since i'm a licensed electrician, it won't pass inspection
should be 4 wire, 2 hots, ground buss and neutral buss
this in it's self isn't unsafe, just not code, would have been code pre-1992.
the wire feeding the sub-panel looks lighter than the main wire
if it's the same size, then your good, if it's smaller
this is unsafe, wire should be sized to the breaker feeding it.
and the exposed romex on top of the sheetrock is a no-no
a short nipple attaching both to the bottom of the panel would have been the way to go
but the main reason for this reply is:
for future reference and to anyone else doing this
there is a breaker that replace 2 standard single breakers
to make 4 breaker, 3 circuit, 120/240/120 circuits
and at $18 each, would have been a lot cheaper to do.