My flight was delayed by 9 hours and once we set off was ok although the plane did appear to be old worn and shabby inside. The delay was due to a generator failure on the previous flight when the plane had to make an unscheduled landing in Naples. On the flight back from Kos (which we were not on the plane), they had to make another unscheduled landing back in Kos due to a generator problem.
Fly on workdays: As many passengers prefer to fly on week-ends, week-end tickets sell first. If you don't book your trip well in advance (2-3 months beforehand) you may notice, for example, that Thursday flights are cheaper than Sunday flights. Some low cost carriers have special promotions on the flights during the week.