The reaction to Obama's visit to Cuba shouldn't be a surprise. The Castros have cast the US in the role of enemy for so long, it must be difficult to convince the population that the horrible imperialists that have oppressed them, starved them, and basically caused all their problems had changed so much.
The transition from pariah to paisano is going to be tough for Cuba. But it'll be tougher for the Cuban government. Their main bogeyman has lost its teeth. Who will they blame their problems on now?
This happened to Panama when the US pulled out of the Canal Zone back in 1999. For several decades before the Carter administration signed the papers to turn over the Canal to Panama, the Panamanian government had maintained that the US was siphoning off money that belonged to Panama because the Canal should have been Panamanian by all rights. Riots had actually broken out and people died in protest of US presence. To this day, there is still an Avenida de los Martires (Avenue of the Martyrs) named in their honor. When the Panamanian government lost its bogeyman, they found it more difficult to hide the reasons for their national problems. They discovered that, like every other nation in the world, their politicians were greedy and corrupt. Their eyes, shielded by the deception of a false enemy, were forced open by harsh reality.
Now Cuba is about to go through the same thing. With the trade embargo disappearing and more capitalism flooding into the island, its communist government is doomed. It will be interesting to see how long the military will maintain its throttlehold on the government.