The fact that he has ended up in No.10 helps avoid too many media questions about the failure of the Tory campaign but that is exactly what it was. An open goal was missed with the impact of the debates probably the focus of too much of the blame. In a recent meeting the Cameron message seemed to be that the strategy was the right one but that the target audiences were proving harder to persuade than expected.
When a party fails to get elected it does call for a degree of introspection. However, it should avoid wallowing in it. The role of timing and circumstance can end up being ignored with a party's analysis of the problems and answers not necessarily wrong but that the electorate is unreceptive, disbelieving of the likely consequences of the mistakes or unwilling to change what appears to be ticking over ok. It is simply hard to remove a government from power when it appears capable, competent and the economy is doing reasonable well. This is what the Tories faced in 2001 and 2005. This can lead to more than is necessary being ditched in the search of electability with a pretty hollow shell being offered to the voters.
Furthermore, the need for a makeover for the Tory party on the scale of New Labour was dubious. The impact of Thatcherism was a genuine shift in British political attitudes, New Labour was much more the compliance with that rather than another shift. Graham Sharp of Critical Reaction is scathing of his assessment of the campaign. The Cameron brand was placed before the party brand but if didn't attract people:
"To win big, all Cameron needed to do was connect with the British public. In this task, he failed alarmingly. This was not just about the detail of policy but about the attitude he presented. The public could not be convinced that here was a statesman rather than a salesman. If Cameron opposed Gordon Brown’s profligacy, why had he gone along with it for so long? If he was a man of his word, why had he reneged on promising a referendum on the Lisbon Treaty?"
This was predictable as pre-election polls showed a deteriorating problem with Cameron's personal brand after the Lisbon treaty decision - not because of the policy decision but because it stopped him looking like something different from the political crowd. Sharp also sees the apologetic nature of the campaign as a core weakness:
"The Cameron strategy was self-denying. The tactics were a greater embarrassment. And embarrassment is the right word, for the message conveyed was that though the Tories were the only party capable of ousting a tired and discredited Labour government, the Conservative leadership was nevertheless embarrassed to be Conservative. The ‘I’ve never voted Tory before but …’ advertising slogan effectively conceded that being Tory was not normal behaviour, but it was perhaps acceptable in an emergency."
He highlights the difference in approach of New Labour did in 1997:
"It will be recalled that the Labour Party had an image problem in the early 1990s. It urgently needed to show the public that it was not just about striking miners and Greenham Common women but was a broad, national force that embraced ‘Middle England.’ So it fought the 1997 general election not upon slogans of self-pity or self-effacing apology but with palpable belief and self-confidence. In its advertising campaign, it adopted the British bulldog and inter-mingled the words ‘new Labour’ with the red, white and blue of the Union Jack. The difference between the campaign masterminded in 1997 by Labour’s Peter Mandelson and in 2010 by the Conservatives’ Steve Hilton could not be greater. The results speak for themselves."