Alan Milburn may be best remembered as the Man with the Plan. The health secretary's resignation coincides with the third anniversary of the publication of the NHS plan, the centrepiece of the Blair government's health reforms which he drew up.

The plan, published in July 2000, and envisaged as a 10-year programme to modernise the NHS and focus it on the needs of patients, will be a lasting legacy of Mr Milburn's stint at the Department of Health. It represents perhaps the high point of his career as health secretary.

His appointment in October 1999 saw him return to the department where he had been a health minister under Frank Dobson. It was seen as a signal that modernisation of the health service would be stepped up a gear.

The NHS plan was the first proof that this was indeed the case. But unlike many of the later policies launched by Mr Milburn, who is seen as something of a political bruiser, the plan was launched in a spirit of consultation and consensus.

Its opening pages were decorated with the signatures of professionals and union leaders from across the NHS - a seeming endorsement of the plethora of targets within.

The centrepiece waiting time targets have been largely met, while it has also given a boost to treatments in key areas such as cancer and coronary heart disease.

Mr Milburn, who has held his post longer than his most famous predecessor, Nye Bevan, will also be credited with winning unprecedented sums of money for the health service.

But controversy has also been a feature of the Milburn era. He has succeeded in steering through the use of private sector hospitals to do NHS waiting list work without facing a huge upheaval, but criticisms from unions and the Labour backbenchers persist.

And the long-running, often vicious attempt to abolish community health councils, a move eventually forced through parliament at the second attempt, showed a health secretary who seemed to have developed a personal obsession with the issue.

As a key Blair ally, Mr Milburn has also fronted the proposal to set up foundation hospitals, which last month prompted a rebellion by more than 60 MPs. His departure leaves the policy as the most potentially explosive piece of unfinished business for his successor to pick up.

The outgoing health secretary will also be remembered for his introduction of the star rating system for hospitals, together with the "naming and shaming" of failing NHS trusts.

This hard-nosed approach, reminiscent of the most brutal days of education watchdog Ofsted, has not won friends in the service.

Nor has Mr Milburn convincingly dealt with the medical profession. He has struggled to win doctors over to waiting time targets. And the issue of consultants' pay is not satisfactorily resolved, despite Mr Milburn's apparent success in carrying through the biggest ever pay system reform for more than a million non-medical NHS staff.

The jury is still out, too, over the ambitious recruitment targets set in the NHS plan: thousand of nurses have been recruited, but it may still not be enough. Fears that numbers of doctors and other key groups of staff are not rising fast enough have not been allayed.

The health secretary's espousal of power for frontline NHS staff and the restructuring of the health service to shift resources towards primary care have been popular.

But the sense that new, often fragile, primary care trusts are struggling to cope, let alone catch up with the rhetoric, has not yet been dispelled.

Continual organisational change and streams of legislation have been somewhat wearying features of Mr Milburn's reign.

Mr Milburn's resignation also removes him from the fray before two other policies from the extreme edges of Blairism can be judged: "franchising" - contracting out the management of failing hospitals - and "payment by results", seen by many as a return to the Conservatives' internal market system where the "money follows the patient".

But the amount of unfinished and politically difficult business to push through will not be the only reason why Mr Milburn's successor faces a tough job.

The new health secretary will have to match the enormous energy, drive and passion that Alan Milburn has thrown into the job throughout his time as health secretary.