Lee, who studied at Cambridge, took over from Goh Chok Tong to become Singapore's third prime minister in 2004, after 20 years in the political arena. Prior to that, he had been in the military, where he attained the rank of brigadier general.

But life hasn't been easy for Lee. His first wife died in the early 1980s and he suffered a bout of cancer the following decade.

Lee, who is the world's highest-paid prime minister, is now married to Ho Ching, the 59th most-powerful woman in the world according to a list. Stanford-educated Ho is the CEO of sovereign wealth fund Temasek Holdings.

Together with his cabinet, Lee has had remarkable achievements over the decade.

"Through business, economic and social policies, Lee ensured Singapore could capitalise on the rise of China and India, and the more general shift of economic power from the West to emerging markets," said Sudhir Vadaketh, co-author of the book .

Lee's team also weathered the 2008 global financial crisis well by dipping into the coffers wisely and initiating policies to cushion both workers and businesses.

Singapore's sometimes topsy-turvy relationship with its neighbour Malaysia, on which it depends for its water supply, has also been stable in recent times.

"Lee had a good working relationship with former Malaysian PM Abdullah Badawi, but I feel he prefers working with current PM Najib Razak as both of them are growth driven," said Professor James Chin, a political analyst at Monash University in Malaysia.

While Singapore is still widely viewed as tightly controlled, it has loosened up under social-media-savvy Lee - but in its own unique way, as critics point out.

For example, protest gatherings - which were outlawed previously - are allowed to take place at a designated park, but only with permits.

But despite doing well on the economic front, the 2011 general election saw Lee's People's Action Party (PAP) put up less than its usual stellar performance at the polls. The party also lost the last two by-elections to the main opposition Workers' Party.

Grumbles over the widening income gap and other policies have also grown louder.

"He has a much tougher job than his predecessors," said Eugene Tan, a law professor at the Singapore Management University. "Twenty years of preparation have not made things any easier for PM Lee's tenure as premier, as Singapore faces its mid-life crisis with inflection points politically, economically and socially."

In a Facebook message to congratulate Lee on his milestone, Singapore's second prime minister Goh added: "But the tougher stretch lies ahead ... You have a tough job. We don't envy you. But we are behind you. All the best, mate."

While survival was the first priority for the country's leaders in its early days, the younger Lee has had to handle an electorate with evolving demands.

"Growth has come with rising inequality, increasing financial pressure for ordinary Singaporeans, and, some argue, decreasing social mobility," said Professor Chong Ja Ian, a political scientist at the National University of Singapore.

"There are also questions over overcrowding, under-investment in infrastructure, and insufficient consideration of the environment and heritage in development planning."

For author Vadaketh, Singapore's "growth-at-all-costs mentality" has had many negative side effects, but authorities are now aware of the problem.

"There is a recent shift in emphasis towards those less fortunate in society, including the poor and handicapped; and towards those who may want to pursue alternative career paths," he said. "Critics may argue it's too little too late, but at least we're headed in the right direction."

Lee had had to "emote" more than his predecessors, Tan said.

"It's a challenge to get the balance of hard and soft power of governing in the right proportions," added Tan, who is also a former lawmaker.

"Singaporeans would like to see firm, principled leadership - certainly a hark back to his father's leadership style but without the authoritarianism," the academic said.

Many observers believe that Lee's biggest mistake over the last decade was letting immigration become a cause of unhappiness for Singaporeans.

"The 'whole-of-government' approach was sorely lacking for a government that prides itself in over-the-horizon policy planning and implementation," Tan said.

As there are perceptions that Singapore's electoral playing field is not level, further calls for a more vibrant political milieu are also expected.

"With 60 per cent of the popular vote but 91 per cent of the elected seats, the electoral system strikes many as being unfair," Tan said, referring to the PAP's scorecard in the 2011 general election.

Transparency was something that more citizens would be demanding - adding yet another challenge for Lee.

"Government decisions, processes, data, and archival records remain difficult to access," Chong said.

Lee, 62, has said he was aiming to step down in 2020.

The party's biggest headache now is finding someone suitably aged to replace Lee in the top seat of a multiracial city state where the vast majority of the population is ethnic Chinese.

Some say 57-year-old deputy prime minister and Finance Minister Tharman Shanmugaratnam would be the best choice, but his age is against him.

He has also said he was not keen on the job.

"For many reasons, including ethnicity, he is unlikely to rise any further," Vadaketh said.

It is widely believed that Minister for Social and Family Development Chan Chun Sing has the best chance of being the next prime minister, with Education Minister Heng Swee Keat also having a shot despite being in his early 50s.

Chan, 46, is a high flier who became the chief of the army at the age of 40.

As Singapore turns half a century old next year, some wonder how the city state will fare under the next political generation.

But if you ask patriotic Singaporeans if their tiny nation will survive the next 50 years, they might reply with a famous quote from the prime minister's father, made during a speech to the nation in 1988. "Even from my sick bed, even if you are going to lower me into the grave and I feel something is going wrong, I will get up," he said.