For New Zealand Gallipoli wasn't nearly as bad as the subsequent Somme, Messines and Passchendaele offensives. It was however the first meat grinder, and thus is listed first in the histories of that war. To be cynical, when studying history, the vast majority of my people don't get past that first chapter and so think it's the major action.
I'm extremely fortunate that my family came into a collection of postcards sent by numerous soldiers from WWI, and it's fascinating reading. The censorship kicked in later on so that for the last 2 years the postcards are simply forms where you could fill in the basics. They would read Dear "blank" I am well/wounded, our supplies and moral is good, thank you for the parcels. Signed "blank".
The Gallipoli and early European ones however are a different kettle of fish and cover the whole milieu of human emotion. One of the striking things in this context is that they don't talk of being anything other than British. There's no thought of some burgeoning independence, of being a separate nation other than Empire. Britain is still referred to as home, the other Empire troops are simply that, no different than battalions from other parts of New Zealand. The Otago battalions viewed the Yorkshire or Sydney battalions as no different than the Wellington one.
The significance of Gallipoli, and be aware this is simply personal observation, has grown from two factors. Firstly our historians/politicians wishing to define a single point of time where NZ came of age. While this may have some aspect of truth in it in a wider context I see no evidence that it was viewed this way at the time or throughout the period leading up to the 1990's.
As referred to above, the mindset of the people of the time was still very much of Empire, not of a new nation. Right up until the seventies I could still find plenty of older people happy to refer to Britain as the 'home country', though there is a subtle but important difference between the original 'home' and this 'home country'.
One of our historians, Michael King, was also dismissive of this single point of time definition. He saw it, as do I, as a gradual change of attitude. His description was that waves of settlers cease to become colonists and become natives when they stop seeing the country as a resource to be exploited and start seeing it as a treasure to be protected. This is a gradual process and is still ongoing, as it always will be unless we become truly isolated through calamity. The idea of Gallipoli becoming the moment when we became a nation is farcical to me, but is promoted as a kindergarten concept, an easy explanation for propaganda purposes.
The second point of significance is that during the seventies and eighties Gallipoli became the place to be seen by backpackers from Aus & NZ in just the same way as Marrakesh and various parts of India became the go-to places for the hippy movement during the sixties. The stories from my contemporaries was that it was the whole Turkish experience, culminating in what was a two or three day booze-up and semi-orgy at Gallipoli as part of a backpacking 'trip'. Only when the international 'noise' this created was sufficient for the NZ and Aus govts to take notice was it reined in and made a formal occasion, in conjunction with the Turkish authorities.