In general, Reconstruction was a failure. However, there are at least two major ways in which it can be called a success.
For the most part, Reconstruction failed badly. If the point of Reconstruction was to improve the lives of the ex-slaves and make them into full members of US society, Reconstruction failed dismally. After a few initial gains, blacks lost almost all semblance of legal equality. They also were unable to achieve any major economic gains because the government was not willing to give them their “Forty Acres and a Mule.” The end of Reconstruction was followed by decades of oppression of African Americans in the South.
However, there are at least two ways to say that Reconstruction succeeded. First, it did force the passage of the 14th and 15th Amendments. These amendments did little to help African Americans at the time, but they did eventually serve as the major legal basis behind the achievements of the 1950s and 1960s. Second, we could argue that the point of Reconstruction was to reunite the country and bring the Southern states back into the Union. In that sense, Reconstruction was a success because, just 12 years after the end of the war, the Southern states were restored to full status as states of the Union.