In his first public comments on the inner workings of the Somare government since it fell on August 2 last year following a backbench coup, Sam Abal says the former government concentrated too much power among its economic ministries.
Mr Abal was Sir Michael's deputy and led his government between mid-March and August 2 while the 75-year-old veteran prime minister was in Singapore undergoing multiple heart operations.
"We didn't give enough attention to the back benches," Mr Abal told AAP.
"I saw that there was a lot of pressure building up over the past nine years (the Somare government was in office.)
"When the opportunity came, the back benches went for it."
That opportunity saw 70 of PNG's 109 MPs form a bloc behind the current prime minister, 46-year-old Peter O'Neill, and his deputy, Belden Namah on August 2, 2011, sparking a constitutional crisis over how Sir Michael was removed.
Mr Abal said another major fault in the governing style of the Somare government was its concentration of power in economic ministries, such as treasury and planning departments.
Sir Michael's son, Arthur Somare, was public enterprises minister until his suspension in mid 2010 pending a corruption investigation.
Government MPs, led by Mr O'Neill, have frequently attacked the Somare bloc for its concentration of power during its term and for trying to set up a "dynasty" without naming Arthur Somare.
Mr Abal two days ago became the first MP to join Australian-born opposition leader Dame Carol Kidu on the other side of parliament.
Dame Carol, currently PNG's only female member of parliament and a former Somare government minister, is retiring at the June election after 15 years in the 36-year-old nation's male-dominated parliament.
With Dame Carol leaving parliament, Mr Abal has offered himself as the alternate prime minister at the next election.
However, the majority of Sir Michael's supporters currently occupy the middle benches.
Mr Abal, who left Sir Michael's side at the start of the year, said he made the decision to join the official opposition because it was important for PNG to have an effective counterweight to government.
He levelled an attack at Mr O'Neill's recent promises of free education and health care.
These promises are populist election winners, he said, and the details have not yet been worked out.
"It brings tension to the bureaucracy when you're unprepared (for these changes,)" he said.
"People flock to the services only to find the orders haven't trickled down."