By Noel Mwakugu
BBC News, Nairobi
Raila Odinga's diehard supporters believed they had voted in a Kenyan president last December, but four months down the line they have ended up with a prime minister instead.
Mr Odinga will be the headmaster of the cabinet
As he was sworn in front of dignitaries including Kofi Annan, the former UN chief who brokered the power-sharing deal with President Mwai Kibaki, Mr Odinga not only began a new phase of his political career, but a new era for Kenya.
"We will ensure that power, wealth and opportunity are [in] the hands of many, not the few," he said after taking his oath of office.
But will he deliver the changes he promised?
This is the million-dollar question on the minds of many Kenyans who are still scrutinising the historically large cabinet that has also just been sworn in.
As a prime minister, his role will be more like a headmaster, watching over the cabinet to see who is doing what.
Less than cosy
It is no secret that the grand coalition cabinet was delayed because of the differences between him and Mr Kibaki on how to share out the portfolios fairly among the new partners.
But when the president announced his new line-up at the weekend, it emerged that his side still maintained key ministries such as finance, security, justice and foreign affairs.
Many supporters of Mr Odinga's Orange Democratic Movement (ODM) feel he has conceded too much.
And some analysts fear the imbalance may harm it in the near future.
It was expected that as co-ordinator of the cabinet, his side would at least have control of the finance ministry as an assurance that his plans would not be frustrated by a hostile manager of the public coffers.
This was not the case.
In fact, Mr Odinga has had a less than cosy relationship with Finance Minister Amos Kimunya.
The new prime minister also faces an uphill task to overcome suspicions that exist between him and ministers belonging to Mr Kibaki's Party of National Unity (PNU) - who fear he may overshadow their boss.
Unlike the president, Mr Odinga is a hands-on man who has a history of being pushy in order to get results, a trait that may antagonise his new PNU allies.
Hundreds of thousands were displaced by post-election violence
Both leaders have pledged that in this power-sharing arrangement there will be a single centre of power.
However, who will wield it is another question.
In 2005, Mr Odinga, then leader of the Liberal Democratic Party, led his MPs out of a pre-election coalition with President Kibaki following sharp disagreements over power-sharing.
And many wonder if Mr Odinga and his team have learnt adequate lessons from that experience.
Despite the delicate process of sharing power, many Kenyans still have great expectations of Mr Odinga whom they view as one capable of delivering long-kept promises.
"We can now consign Kenya's past failures of grand corruption and grand tribalism to our history books," he said on Thursday.
His outspoken nature has earned him a reputation as Kenya's justice crusader.
During last year's election campaign, he accused Mr Kibaki of being insincere in failing to fight deep-rooted corruption in government.
So many will expect him to reduce it to a minimum if not eradicate it.
And it may come with a high political price as close confidants may have to be sacrificed along the way.
Ethnic tensions remain high following the bloody post-election violence and many are looking to the new government to lead the way in healing the nation.
Mr Kibaki will stand down as president in 2012
The buck stops with Mr Odinga as the prime minister to ensure that this process begins right at the heart of the civil service, whose upper echelons are made up of people mainly from central Kenya - Mr Kibaki's heartland.
The chaos Kenya witnessed is arguably the result of historic injustices including unfair land tenure systems and the unequal sharing of resources between the country's more than 40 ethnic groups.
As it stands, the government's first priority will be resettling more than 300,000 people who fled their homes because of the violence.
Mr Odinga will need tactful negotiation to mend the fences among the affected communities.
Analysts argue he will also need to show his teeth to keep to his promise that "power will forever reside with the people of Kenya".
Political reforms will include a new constitution to guarantee that power is devolved and true democratic principles take root.
But when all is said and done, all eyes are already turning to 2012 when President Kibaki will have to stand down after two terms in office.
Mr Odinga will then have the opportunity to stand for president depending on his record as prime minister.
The succession game has just begun.