Some are better than others. Below are my reviews of each story. Overall, I'd probably give the whole collection a 3.5, but decided to round up since I didn't hate any of them. If you read only one, make it Spring in Skiathos.
Spring in Skiathos - 4/5 Fun light beach read. No language or sex scenes. I enjoyed the peek into life on a small Greek island. While the main romance is slightly predictable, the back story is a little more complex. Looking forward to the next one in the series!
Summer in Santorini - 3/5 A fun light beach read. Not quite as good as the first one in the series, but still enjoyable.
Autumn in Crete - 4/5 I've always had a weakness for stories set in Crete thanks to the old Hayley Mills movie "The Moon Spinners." I found the information about the island's topography interesting. I also enjoyed the romantic plot. A fun, easy beach read.
Winter in Rhodes - 2/5 I found this installment in the series very stilted and amateurish. The vocabulary & sentence structure just weren't as good as the 3 previous books. I'm glad I didn't read this one first or I wouldn't have bothered with the other ones.