Thanks to a quirk of humankind and not of nature, the international date line swings eastward from its north-south path down the middle of the Pacific Ocean just enough to make the last Polynesian monarch the first sovereign to see the light of each new day. When King Siaosi (George) Tupou V of Tonga greets the dawn and looks out on his realm from the veranda of his whitewashed Victorian palace, he sees a country of low but fertile islands, of gorgeous sandy beaches, and of colorful coral reefs waiting to be explored.
His nation is protected -- but was never ruled -- by a Western power. Like Samoa to the north, Tonga has managed to maintain its Polynesian culture in the face of modern change. The Tonga Visitors Bureau is spot on when it says the kingdom "still remains far away from it all; still different, still alone, and to the joy of those who find their way to her -- essentially unspoiled."
While this description is true of the flat main island Tongatapu, it is even more applicable to Vava'u and Ha'apai. Vava'u is a group of hilly islands whose fjordlike harbor makes it one of the South Pacific's most popular yachting destinations. The low islands of the Ha'apai group seem to have changed little since the crew of HMS Bounty staged their mutiny just offshore in 1789. Visiting Vava'u is extremely pleasant to the eyes, and you should make every effort to see it and its multitudinous islets.
Along with a taste for adventure, I would be sure to bring a sense of humor to Tonga. Things don't always go according to plan here. The local airline might not come to get you, the electricity might suddenly quit, and the tap water might be turned off during your lukewarm shower (not that you can drink it when it's running). You'll see multitudes of dogs, chickens, and pigs almost everywhere, even wandering the streets of Nuku'alofa, the capital. But if you take the quirks of humankind with a smile, you will enjoy your time in Tonga, during which you will get a most fascinating glimpse into the way things used to be out here.