Went there for the Shetland Folk Festival in March/April a few years ago and it was well worth the visit. The music began on the ferry from Aberdeen with an all-night session. People were friendly and I was amused and gratified to find all people from south of Shetland dubbed as "Britishers" - ie no Anglo-Scots rivalry there, Shetlanders have their own independent point of view. The festival involves musical events all over the islands and it is worth traveling to the smaller and more remote villages for a local atmosphere and dancing all night. The other big event is the Viking festival where people dress up as vikings and sail longboats.
The islands are rich because of a good deal they struck with the British over the oil in the North Sea, and have built many stadiums and concert halls. They are fairly barren and have virtually no trees, but this landscape is made up for in the warmth of the welcome, particularly if you like music. There is an incredible amount of musical talent on the islands. Shetlanders have a great sense of humour but be prepared to have people tell you tall stories to try to catch you out. They have a lovely way of talking with Norse dialect words.
Above all, never call the place "the Shetlands" but always "Shetland" or "the Shetland Islands".
