Unlike his boss the president, who lamely resubmitted his name for confirmation after the election results made such a move utter nonsense, John Bolton read the handwriting on the wall and submitted his resignation, rather than remain as Dick Cheney's Bronx salute to Congress.
There isn't anything wrong with a UN ambassador who is conservative, and thinks that the world body is of limited value and in need of reform. But Bolton's pre-appointment record indicated outright hostility and contempt towards the UN. He himself had a disregard for facts and used national security information to settle political scores and undermine his superiors while working at the State Department. And in the short time while he was at the UN, he seemed to undermine any attempt at collaborative work, thereby diminishing his chances to convince others that the United States was correct in its positions.
This may be exactly what the Cheney White House wanted, but that doesn't warrant keeping Bolton as an ineffective voice for the United States on the world stage. Like so much else with this administration, we have basically wasted years at the UN since John Danforth left, at a time when we desperately need allies and open communication, as well as the ability to persuade others.