I feel that Shetland is best approached by sea on one of the daily ferries from Aberdeen. When we first started to go up in the 1980's we traveled on the St Clair , in 2002 Northlink took over and started running the Hjaltland and Hrossay ferries. However in July 2012, the Serco Group took over running the service.
With the possibility of seeing, various seabirds as well as dolphins and whales, ferry travelling is the best introduction to the Northern Isles. It may be 340 km from Aberdeen and take 12 hours overnight, but the slow approach as it glides up the east coast of Shetland gives you time to absorb the landscape and feel the wind in your face, a feature that you will have to get used to.
It not all plane sailing, we did travel up on the St Clair in a force 9 gale one year , and I have seen YouTube videos where people were unable to stand up in very rough conditions. But if you decided to go by plane you have to contend with the fog and many a time people have been transferred to the ferry as there was no hint that the fog would lift from Sumburgh airport.
The sea has to be respected and many a ship have been broken by the force of the storm. This one going down the day before we arrived in 2011. The coastguard is very busy in Shetland and well supported by the islanders, with a yearly gala held both in Lerwick and Aith to raise funds
The sea rules the way of life to all living in Shetland, many depend on the sea for a living, seabirds dependent on the sea for food and with no area being more than three miles from the sea, daily life is governed by the sea & weather and not by materialistic items as it is further south.