Or is it seen as something that can be challenged or even, in parts, refused?
The Catechism is a sure norm for teaching the faith: it is a sure and authentic reference text for teaching Catholic doctrine. Thus it is official doctrine, inasmuch as it records what the Church teaches. That is, the Catechism puts forth what the doctrine is; it is not actually doctrine itself.
However, because it represents the teaching of the Church's faith, it is not something to be challenged by Catholics. It is an authentic statement of the teaching of the Church.
All of this is what is meant by "preparing local catechisms": the different Bishops' Conferences [which are generally arranged on a national basis] can prepare their own translation of the Latin original; YouCat, the Youth Catechism, has also been published. There are non-English translations too. Provided that these local versions — each prepared for particular circumstances — also represent the teaching, they do not challenge the Catechism. The Catechism is an authentic statement; it's not the authentic statement. But because it is an authentic statement of Catholic doctrine, it's a useful tool for stating what that doctrine is, and for comparing other teachings to see whether they are consistent with Catholic doctrine.
I am sure there are parts which non-Catholics might take issue with; and by the same token there will be parts which they might be surprised to find it does in fact contain.