In 1981 I went from Mykonos to Delos on a very small motor boat. The passengers were strapped into place by a thick rope. The sea was rough. I was lucky not be starnded on the island. A French girl once told me about a school trip she had been on to Delos. All they had to eat were rabbits caught by one of the custodians of the island. After they arrived a storm blew up, and they could not leave for several days.
On my next trip I went on a much bigger boat, with more than one deck level.
Guide books will tell you what to see on Delos - it is a fascinating place, and there is too little time to enjoy the island between the arrival of the first boat and the departure of the last. On my two visits I have been lucky - there have been no cruise ships in. The atmosphere of the island would change completely if it was overrun with 100s (or 1000s) of tourists.
Mykonos is not one of my favourite islands - but I would put up with a night or two on Mykonos to enable me to see Delos. Delos is an archaeological site, and there is no accommodation for tourists, storm stranded or not!
