The meeting was the first to be held under new Governor Haruhiko Kuroda, who has pledged to do whatever it takes to achieve the 2 percent inflation target adopted by the BOJ in January.
Financial markets gave their swift verdict following the announcement: Japanese shares reversed their falls to close more than 2 percent higher, while the yen tumbled almost 2 percent to around 95.20 per dollar.
"The Bank of Japan is doubling its balance sheet going from 130 trillion yen ($1.36 trillion) to 270 trillion yen by the end of 2014. The buying program goes right out to 40-year JGBs. It's going to trigger massive allocation shifts, and not just in Japan," Bill Blain, a strategist at brokerage Mint Partners, said in a note.
Some analysts remained skeptical as to whether the BOJ would be able to deliver on its inflation target despite the breadth and scale of the measures unveiled Thursday.
"Throwing in the kitchen sink to fight deflation doesn't guarantee that we will get to 2 percent inflation," said Vishnu Varathan, market economist at Mizuho Corporate Bank.
(Read More: Japan Just Might Be Set to Open a New Chapter)
"Achieving that target will depend on a broader economic recovery and some restructuring taking place," he added.
Analysts add that because deflation is so entrenched in Japan, turning that situation around will not happen overnight, even with a radical overhaul of monetary policy.
Latest data shows that Japan's core consumer prices fell 0.3 percent in February from a year earlier.
Missing the Point?
Others argue that the talk about whether the BOJ can achieve its target misses the point.
"There is always going to be skepticism about whether the BOJ will succeed or not," said Shane Oliver, head of investment strategy at AMP Capital in Sydney. "The key issue over the last few years has been that the BOJ has not been aggressive enough and the fact that they are trying a lot harder is a positive sign."
Oliver added: "There was a fear that they would not deliver and that was reflected in the volatility in Japanese share markets this week."
(Read More: BOJ Sparks Dramatic Turnaround in Nikkei)
Japanese stocks suffered losses earlier this week, while the yen strengthened amid some concerns over whether Kuroda would be able to achieve a consensus on the nine-member BOJ policy board for unorthodox monetary policy measures.
Up until now the BOJ has had a reputation for a conservative stance and the fact that the decisions taken on Thursday were unanimous was seen as a positive sign.
"Unanimity is very important indeed because central banks around the world, when they put out strong statements of intent, when they signal a new change in direction, its far more powerful, far more potent if it can do that with a united front," said RBC's Ashley.
Oliver at AMP Capital said signs that aggressive monetary stimulus by the Federal Reserve was helping revive the U.S. economy, suggested that the BOJ could do the same.
(Read More: Poll: Can BOJ Achieve Its 2% Inflation Target?)
"Whether they (the BOJ) are going to hit 2 percent inflation in two years' time is an open question. But the evidence from the U.S. which has practiced very aggressive monetary easing is that it does help," said Oliver.
"The trouble with the Bank of Japan is that they haven't been doing it and now they are, so I would be inclined to give them the benefit of the doubt," he added.
By CNBC.Com's Dhara Ranasinghe; Follow her on Twitter: