Despite the forbidding exterior they are no harder to open up then an avocado. I would describe it has mildly sweet and custardy. Here's one way to use a dragon fruit http://food52.com/recipes/12279-cinque-doigt-marie-s-dragon-fruit-fizz

Pretty amazing to look at but not the most flavorful of tropical fruits.

Pretty bland, I think.

It depends how ripe they are inside. A little bit like a not very sweet pear