Hi Mrs Moo,
Never been in May or June but I'm assured that it really is a good time to visit Malta. I suppose prices are lower because it's not a popular time to go and as Mark and Nicky have said it is in school term time.
It also happens to be when most of our schoolkids are sitting their exams so it's even more unlikely that many people, ourselves included, would choose this time to take a holiday. However, when our son has left school I guess we'll take advantage of the cheaper prices and try a break in June.
If you do go let's know how you get on,
Trev