In truth, it’s too early to tell how big a deal these letters are in terms of how they’ll affect the narrative of the Whitlam dismissal. After all, the letters were still only released last week at time of writing, and it simply takes time to fully understand a large cache of historical information. New academic journal articles and books that take into account this information are months away at the very earliest. For starters, beyond simply knowing what is in the letters, they still need to be carefully contextualised and compared with other sources of information in order to understand better how the letters reflect the events occurring at the time. Secondly, they need to be analysed by someone who is familiar with the protocols and conventions of such correspondence and what they were expected to say and not say in such letters.

In a previous answer to a now deleted question, I discussed Professor Jenny Hocking's campaign for the release of the letters in context of discussing Murdoch's role and the CIA's role in the Whitlam dismissal. Hocking's history of the Whitlam government (published in 2012) is well-regarded, and Hocking is probably one of the people best-placed to analyse such letters. In a Sydney Morning Herald opinion piece published on July 14th (very soon after their release to the public), Hocking says that:

What is pivotal throughout these letters is that the Queen, through her private secretary [Sir Martin Charteris], engages with Kerr on these inherently political matters, even advising him on the powers of the Senate and, critically, the existence and potential use of the contentious and contested reserve powers to dismiss the government...these critical letters provided Kerr with the advice and comfort he needed to feel secure that the Palace accepted the existence and potential use of the reserve powers as he moved towards dismissing the Whitlam government.

Broadly speaking, Hocking doesn’t seem surprised by what she saw in the letters - the Queen’s representative not showing any sign of outrightly controlling events or being told in advance of the dismissal, but the representative also clearly pushing Kerr in a certain direction, and clearly going to what is clearly something of a grey area in terms of the role expected of the Queen and her representative in a constitutional monarchy - and that surprise is likely not least because one letter along those lines was already present in Kerr’s archives (which is why Hocking wanted to see the rest of the letters in the first place).

Malcolm Farnsworth who runs the WhitlamDismissal.com website amongst other useful Australian political information websites, had a Twitter thread on his initial reactions to reading all of the letters, in which he said that:

5/- Most of all, though, for me, there’s a sense of transactional business always going on [in the letters]. The Palace needs (and gets) plausible deniability. In the end, they don’t really care about Whitlam or Fraser. Kerr gets cover and, he hopes, kudos for resolving a difficult impasse.

6/- The Palace acknowledges they are a constitutional monarchy. They must take the prime minister’s advice or they’re finished. But they know how to massage that reality, how to delay and obfuscate. We can assist you, Sir John, just don’t drop us in it.

It’s also odd to think that people mentioned in the letters (other than the Queen) not only are still around, but now have blogs, but John Menadue was a public servant who was head of the Department of Prime Minister and Cabinet between 1974-1976 (i.e., both under Whitlam and Fraser). Menadue was mentioned several times in the letters and also corresponded himself with Charteris. In a blog published today, the 85-year-old former public servant seems to be very strongly of the opinion that the Queen was not only formally responsible for Charteris’s actions, but likely knew exactly what was going on:

It is nonsense to say the Queen was not involved. Her favourite courtier [Charteris] and she carry joint responsibility for the sacking of a government that had a clear majority in the Australian House of Representatives. A foreign power intervened in our political processes.

Much less scathing of the Queen and Charteris is a piece in the Conversation by Anne Twomey, a specialist on constitutional law and history. Twomey is less sympathetic to Whitlam’s predicament and more inclined to think that constitutionally, Charteris behaved quite properly:

...no, the queen did not direct Kerr to dismiss Whitlam. He was not encouraged to do so. He was only encouraged to obey the Australian Constitution, which is something we all should do.

Between these quotes, you probably get a sense of how the letters are initially being taken by astute observers who are very familiar with the events of 1975. But, that being said, we’re most likely best off waiting until the content of the letters have been analysed more fully.

After all, Hocking also says in the op-ed that

This is just the first day of viewing these extraordinarily significant letters and there is much still to see and even more to assess. As we delve deeper into them, just as important as what is in the letters will be what isn’t there – the gaps, the events and people who should be but aren’t.

Similarly, Farnsworth ends his twitter thread with:

10/ - The letters need to be read again. They need to be digested and placed against the weight of the evidence, especially the bits Kerr never mentions. (Justice Mason, you do have a duty to history.)

11/- Maybe I’ve got it all wrong...