Wilmott has a knack of explaining a concept intuitively so you "get it", then showing the maths behind it. Far too many other authors take you through pages of derivations, leaving you with a equation which leaves you none the wiser.
If you want to impress your boss or friends by leaving a complex, dense looking tome of seemingly indecipherable maths on your desk, go elsewhere.
But if you want a light-hearted, consise but thorough introduction to quant finance, I'd highly recommend his book.
Note the similarity between the 1 volume ('introduces') and the 3-volume ('on') Wilmott textbooks. You don't need both - the 3-volume is simply the 1-volume with some extra depth in places.