Barring his most bitter critics, the widespread view seems to be that Modi, who turns 64 Sep 17, is proving to be a prime minister the country has lacked in recent decades - strong, decisive and pro-active. His Bharatiya Janata Party (BJP) certainly thinks so.
"Modi has taken bold decisions and has provided the direction on which government policies will unfold in the months and years to come," said BJP spokesman G.V.L. Narasimha Rao, who interacts closely with the veteran politician.
"There is a sea change in the last three months in the way the government functions," Rao told IANS, comparing it with a decade of Congress rule. "Modi has empowered the bureaucracy and given a clear direction to the political leadership."
After presiding over Gujarat for 13 long years, Modi created history in May when he led the party to a stunning electoral win. The BJP became the first party in three decades to get a majority of its own in the 545-seat Lok Sabha, crushing the Congress to a humiliating 44 seats.
Although Modi formed a coalition government after being sworn in on May 26, it is Brand Modi that stands out. Some of his decisions are plainly visible.
Besides giving a new direction in governance, the government has started on the gargantuan job of financial inclusion of 1.2 billion Indians, to eradicate what Modi calls "financial untouchability" from the country, embarked on the difficult path of judicial reforms, displayed the will to hike rail fares and axed the decades-old Planning Commission, formed a special team to retrieve black money stashed abroad, set up a portal for citizens to directly interface with the government, and come up with a ministry of entrepreneurship to promote citizen-driven growth.
Ajay Shriram, president of the Confederation of Indian Industry, told IANS: "Investor sentiment is back as the new government demonstrates high commitment to growth and reforms. In our interactions with ministers and officials, we have found strong willingness to consider industry's views and take up out-of-the-box solutions."
Modi has told ministers to curtail all wasteful expenditure and virtually banned foreign jaunts. All policy decisions are vetted. Do's and don'ts have been issued to ministers and officialdom. Different ministries can no longer work at cross-purposes.
And Modi the politician - who rose through the ranks after having once sold tea at a small town railway station in Gujarat - turned the customary Aug 15 Independence Day speech to connect with the people like no prime minister has done, underlining, among others, the basic social and civic values of cleanliness and hygiene.
In what has taken most Modi watchers by surprise, the prime minister has shown a keen interest in foreign policy that saw all SAARC leaders, as well as of Mauritius, fly to New Delhi for his inauguration. He has made quick trips to Bhutan and Nepal to repair ruptures in relationships, taken a strong stand on Tamil rights in Sri Lanka, and is determined to step up ties with not just Japan but also China and the US , although Washington had shunned him for years on account of the 2002 Hindu-Muslim riots in Gujarat.
Ashok Behuria, the Pakistan expert at the Institute for Defence Studies and Analyses, told IANS that the Modi government has shown "some amount of courage" to call off the secretary-level talks with Pakistan after Islamabad's high commissioner met Kashmiri separatists in New Delhi.
"But this could have been done in a smarter way," he added, and suggested that the foreign secretary could have conveyed India's stand in an official manner to Pakistan. According to him, Narendra Modi is "drawing his red lines" vis-a-vis India's engagement with Pakistan, an action that drew some mainstream media criticism but was widely hailed on social media.
The first major crisis to hit Modi was the abduction of 44 Indian women nurses by Sunni insurgents in Iraq. But the government managed to have them freed. But an unspecified number of Indians remain hostage in Iraq.
Despite Modi's popularity, the BJP has suffered reverses in recent assembly by-polls, from Uttarakhand to Bihar. One ally, the Shiv Sena, has taunted the BJP. With four states going to the polls this year, the BJP is under pressure to show that the Modi wave of May was not a fluke.
Not everyone is impressed with Modi's 100 days.
Critics underline that there has been a spurt in communal riots since Modi took power, that some BJP leaders have poured venom against Muslims, that the annual budget unveiled in July was not reform-oriented as many thought it would be and, contrary to expectations, there has been no big-bang economic policy announcement.
"The government's performance has been extremely disappointing in the first 100 days," Congress spokesperson Sanjay Jha told IANS. "They had raised a lot of hype and made exaggerated promises. But there is nothing to show on the ground.
"The by-election results show people are already disappointed," he said.
Others have faulted the Modi government for forcing governors of several states to quit simply because they were appointed by the earlier government. The elderly Kamla Beniwal, who as Gujarat governor enjoyed frosty ties with then chief minister Modi, was first shunted to far away Mizoram and then, within days, sacked.
After using the media extensively during the election campaign, Modi is now keeping the media at an arm's length and has discontinued the practice of taking a large media party on foreign tours.
The BJP's Rao, however, swears by Modi the prime minister.
"Modi is a man with a very, very clear vision, a man who knows what is the road he has to travel, what is in national interest. The strong point about him is that he does not get unnerved by criticism as long as he knows he is on the right track."
"Modi is seen as a star in the international scene," Rao said. "Everyone recognizes that India now has a strong and decisive prime minister who will be there for years to come."
"All this is striking when you compare it with the Manmohan Singh government," he added. "The earlier PMO was like the Malaysian plane which disappeared. There was no sense of direction in UPA II."
Mukhtar Abbas Naqvi, one of the handful of Muslim leaders in the BJP, told IANS: "In these 100 days, the government has both performed and reformed. We have been able to show the world that a new Bharat is emerging."