Reconstruction refers a twelve year period after the Civil War, lasting from 1865-77. During this time the North implemented its plans to rebuild the newly conquered South, to reorganize it after the end of slavery, and to reintegrate into the United States.
In terms of reintegration of the eleven rebel states into the union, this was an unqualified success. The states were readmitted seamlessly and the country knit back together as a strong political whole. Legally, too, the period was successful in granting blacks full and equal citizenship under the law, including the Constitutional right for all black men to vote. The Constitution was also amended to bar slavery, except in prisons. These were extraordinarily important and decisive acts.
As long as the U.S. army had a presence in the Southern states, blacks were offered a measure of protection and, initially, were allowed to vote and be elected to government offices. This time period and its increased rights had a great impact in forwarding the movement to integrate black Americans as equal citizens.
However, when it came to reorganizing and rebuilding the Southern economy and ensuring that blacks would be able to exercise their newly won rights, coexisting as equals with whites, Reconstruction failed. It ended too soon, and ultimately, allowed "state's rights" to trump federal interests. Once the former southern slave-owning classes realized they could seize control of their legislatures and enact whatever laws they wanted, they worked aggressively to disenfranchise blacks and turn them into second class citizens little better than slaves. The lack of a strong industrial base due to decades of agriculture also meant that, to this day, some former rebel states remain among the very poorest in the nation.
The record, therefore, remains mixed: when the federal government acted cleanly and strongly, such as in fully reintegrating the southern states and granting former slaves full citizenship, Reconstruction was a success, but where it was weak in implementing its intentions, such as backing down after a strong start on enforcing black equality as more than a paper concept, Reconstruction failed.