Castro had written in the first of two online columns that the US had announced the repeal of "several hateful restrictions," but had stopped short of real change.
"Of the blockade, which is the cruellest of measures, not a word was uttered," the former president wrote.
"In effect, it's a form of genocide. Harm cannot only be measured by its
economic effects. It has a constant cost in human lives and it causes our citizens painful suffering," Castro said.
The former leader stepped down from the presidency in February last year, leaving Raul Castro, his brother, installed as Cuban president.
Previously, Cubans living in the US could travel to the isolated Caribbean nation only once a year and only send $1,200 per person in cash to family members there.
And under rules enacted in 2004 by the administration of George Bush, Obama's predecessor, Cuban-Americans could travel to the island just once every three years and could send only $300 to their relatives.
The two nations have not had diplomatic ties since 1960, when the US severed them following the revolution under Fidel Castro.
But Castro said that Obama would not do the damage believed to have been done by his predecessor.
"We do not have the slightest desire to harm Obama," Castro added.
"He doesn't have responsibility for what occurred and I'm sure he won't commit the atrocities of Bush."
Analysts believe the change in US policy could usher in a new era of openness between the two countries.
But among Cubans there was a mixed reaction to the news.
Many saw the changes as a welcome humanitarian gesture.
"You can imagine what it is like to have a marriage by telephone," Berta Maria Mayor told the Associated Press as she waited for the charter plane carrying her husband back to Cuba for the first time in three years.
"I'm in love with someone I barely get to see," the 45-year-old added.
However, Jose Pilar Ramos, who was looking for work in Havana said his cousin in Miami did not have enough money to visit Cuba, regardless of what US law now allows.
"Obama can do what he wants, but the problem is here. People don't want to work for $4 a week, even if they get more money from family members over there," he said.