I bought this for my Son this Christmas (just before turning 4yrs old).
A real hit - he has managed to concentrate on it for anything up to a full 1hr and has come up with some amazingly creative ideas.
Obviously it needs some supervision to avoid the small tacks going all over the floor ... but a lovely toy.
My only criticism is that the cardboard box is a bit flimsy .. but in any case I think it's the type of toy that deserves to be kept in a nice wooden box which would only add to the tactile experience of this toy.