Pretty accurate actually. Franco assumed Juan Carlos would be a faithful successor to his ideals, perhaps because Juan Carlos' grandfather, King Alfonso XIII had himself supported Franco's coup d'état in 1936. Now the issue here is that he got patriotic in excess, in that, since Spain was traditionally a monarchy, Franco intended to restore Spain to its roots by naming Prince Juan Carlos as his heir. He should have instead named somebody that was in fact, actually involved with the ideas of his movement. Perhaps Prime Minister Carlos Arias Navarro, or Minister Manuel Fraga.
Arias Navarro was the Prime Minister when Franco died in 1975, but since Franco named Juan Carlos as his successor and not him, the King had the authority to dismiss him, and instead he appointed the more liberal Adolfo Suárez to be Prime Minister. Then in 1977, the Ley de Amnistía was passed, which, though it granted immunity to all Francoist officers for their actions during the regime, it also exonerated all the socialists and communists that had been exiled from Spain under Franco. Thus, in 1977 the first post-Franco democratic elections were called, in which both the Spanish Socialist Workers' Party and the Communist Party of Spain participated and won seats in the Congress of Deputies, though thankfully neither won. Adolfo Suárez's Unión de Centro Democrático ("Democratic Centrist Union") won the election and thus he was reaffirmed as Spain's first democratically elected Prime Minister.
Then in 1978, the Spanish Constitution was redacted. Spain was, and still is, a very divided nation ideologically and culturally, so Suárez's party sought to create a consensus constitution that could unite all Spaniards and leave past grievances behind. For this, seven men were called to redact the Constitution: three belonging to UCD (Unión de Centro Democrático), one belonging to PSOE (Spanish Socialist Workers' Party), one belonging to the Communist Party, one belonging to Alianza Popular (this was Manuel Fraga, former Francoist minister, now leader of the main right-wing party in the country), and one representing nationalist minorities in the Basque Country and Catalonia. So the Constitution is sort of a mess to begin with because you had two of the seven guys who wrote it that were openly Marxist, plus one that was a separatist. Now, conservative Manuel Fraga was also one of the seven redactors, but frankly, that's perhaps what saves the Constitution from being completely tolerant to communism.
In 1979, the first constitutional elections were celebrated and PSOE and the Communist Party both increased their number of seats in the Congress, though so did UCD, with Adolfo Suárez again being confirmed Prime Minister. Then, in 1981, Suárez resigned from office amid internal divisions within his party, and Deputy Prime Minister Leopoldo Calvo-Sotelo was chosen to succeed him. However, during the process of investiture, on 23 February 1981, occurred what came to be known as an unsuccessful coup d'état. A group of armed members of the Guardia Civil, led by Lieutenant Colonel Antonio Tejero, stormed the Congress and took all of its members as hostages, as over two thousand collaborators militarily occupied the city of Valencia. Eventually, the coup was unsuccessful after King Juan Carlos made a televised statement condemning the perpetrators and reaffirming his support for the Constitution. Tejero and a few other collaborators were sentenced to prison and Calvo-Sotelo was confirmed as Prime Minister two days later.
Following internal divisions of the UCD party, with both liberal and conservative wings growing apart from each other, Suárez himself left the party to form Centro Democrático y Social (Social and Democratic Centre). With this split among UCD voters, and growing fear in the population that they were going to regress to authoritarianism after six years of transition to democracy, the Spanish Socialist Workers' Party won the 1982 election in a landslide, with 202 out of 350 seats in the Congress. UCD went from 168 seats to just 11. PSOE would remain in power until 1996, when they were finally defeated by the Partido Popular (People's Party), which was a right-wing party formed by the previously mentioned Manuel Fraga. Since 1982, the Spanish government has consistently been going back and forth between the socialists and the populists, with the socialists being shamelessly corrupt and authoritarian, often violating the constitution, and the populists being generally scared of social scrutiny enough that they won't actively undermine the left's excesses.
In short, yes, Franco committed a terrible mistake by naming Juan Carlos as his successor. It was like a shepherd delegating a wolf to take care of his sheep. Juan Carlos allowed a transition away from the Francoist ideals, the amnesty of socialists and communists, followed by their legalization and representation in the Constitution, and now there's a socialist hellhole legitimized by the tolerance of the Constitution to communists and nationalist left-wing separatists in Catalonia and the Basque Country. Should have named an actual member of the Francoist government as his successor.
