What was George Washington’s greatest achievement as president? What was his worst failure?

After the Revolutionary War, George Washington wanted to retire to Mount Vernon and leave the governing of the new country of the United States to others. However, he was unanimously elected as the first president, and he reluctantly agreed to assume office. He was inaugurated on April 30, 1789, in New York City.
Perhaps Washington's greatest achievement as president was the forging of a united nation out of the former colonies that constituted the United States. He refused to become involved in the divisions of political parties, and when he toured the country, he impartially toured both the northern and southern states. He chose to include diversity of opinion in his cabinet of advisors, even though it meant that people at opposite ends of the political spectrum, such as Thomas Jefferson and Alexander Hamilton, were often squabbling. In order to maintain the unique national identity of the United States and give it time to grow strong, he maintained a policy of strict neutrality in foreign relations, in particular when war broke out between France and England. All of these policies and decisions served to keep the fledging country unified and secure in the vulnerability of its youth.
Possibly his greatest failure, at least in his own estimation, was his inability to keep partisanship out of American politics. He refused to be a member of a particular political party, and growing ideological divisions between opposing parties deeply saddened him. In his farewell address upon his retirement from public service, Washington gave a final warning against the dangers of a party system:

I have already intimated to you the dangers of parties in the State, with the particular reference to the founding of them on geographical discriminations. Let me now take a more comprehensive view and warn you in the most solemn manner against the baneful effects of the spirit of party generally.

As we can see, Washington considered it a failure that by the time he left office, American politicians were splitting into party divisions.
https://www.britannica.com/biography/George-Washington/The-Washington-administration

https://www.history.com/topics/us-presidents/george-washington

https://www.presidency.ucsb.edu/documents/farewell-address