Specifically, the following section is seen as problematic:
First, take a look at #839 and #840, the discussion of the relationship between Judaism and Christianity. It says the Jewish People were "the first to hear the Word of God." That's pretty clear - they definitely heard the Word of God.
The Church and non-Christians
839 "Those who have not yet received the Gospel are related to the People of God in various ways."325
The relationship of the Church with the Jewish People. When she delves into her own mystery, the Church, the People of God in the New Covenant, discovers her link with the Jewish People,326 "the first to hear the Word of God."327 The Jewish faith, unlike other non-Christian religions, is already a response to God's revelation in the Old Covenant. To the Jews "belong the sonship, the glory, the covenants, the giving of the law, the worship, and the promises; to them belong the patriarchs, and of their race, according to the flesh, is the Christ",328 "for the gifts and the call of God are irrevocable."329
840 And when one considers the future, God's People of the Old Covenant and the new People of God tend towards similar goals: expectation of the coming (or the return) of the Messiah. But one awaits the return of the Messiah who died and rose from the dead and is recognized as Lord and Son of God; the other awaits the coming of a Messiah, whose features remain hidden till the end of time; and the latter waiting is accompanied by the drama of not knowing or of misunderstanding Christ Jesus.
841 The Church's relationship with the Muslims. "The plan of salvation also includes those who acknowledge the Creator, in the first place amongst whom are the Muslims; these profess to hold the faith of Abraham, and together with us they adore the one, merciful God, mankind's judge on the last day."
The Jewish faith "unlike other non-Christian religions is already a response to God's covenant." Hmmm... What other non-Christian religions might that be a reference to (hint: see CCC #841)?
The Jews are already sons, already in irrevocable covenant with God. They have very similar expectations to Christians. They get two paragraphs of discussion, quite a bit more than everybody else gets.
Contrast this treatment to how the Muslims are treated in CCC #841.
Especially, notice two things about that particular article:
1) It doesn't say Muslims DO hold the faith of Abraham, it just says that THEY profess to hold the faith of Abraham. The Catechism in no way says they are correct in their allegation - it just notices that they say it, and then - with a deafening silence - fails to confirm that they are correct.
2) It also says - without being obvious about it - that Muslim theology about Jesus is completely wrong.
You'll only notice point two if you know a little something about Muslim theology (keep in mind that the Church has been dealing with Muslims, sometimes at the point of a sword, since at least 632, so She has some passing acquaintance with Muslim theology).
You see, both Christians and Muslims believe that Jesus is the Judge on the Day of Judgement.
But, of course, Muslims don't think Jesus is God while Christians know He is.
So, when CCC #841 says "together with us they adore the one merciful God, mankind's judge on the last day", the CCC affirms that Jesus is God and essentially says that the God the Muslims worship MUST be Trinitarian (or He wouldn't be God).
To put it another way, since Jesus is God, He is necessarily Judge.
Muslims believe Jesus is Judge, then insofar as they understand that He is Judge, while they may not realize it (because they aren't too bright), by saying Jesus is Judge they admit that He is God.
In short, the CCC says Muslim theology and Christology is terminally screwed up. The CCC is slamming the Muslims for being ignorant slobs, but it's doing it in the nicest possible way.
And, since it is in the CCC, this statement that Muslim Christology is WRONG is a point of Catholic doctrine - that is, all Catholics must accept and believe that Muslim theology is wrong.
Now, why would the CCC be so delicate in how it phrases things?
Keep in mind that in 2000 years, there have been a total of TWO(2) - count 'em, TWO - universal catechisms. The first came after the Council of Trent and served for nearly 400 years by itself. It is still considered an authoritative reference on doctrine - nothing in it is abrogated.
This new catechism will undoubtedly be in service for centuries as well. Who knows who will read it in the future or what chips may be on which shoulders when it is read? So, the newest CCC figures discretion is the better part of wisdom.
It says as many nice things as it can about non-Christian faiths. There's a lot of nice things that can be said about Jewish theology and... well... what can be said nicely about Muslim theology was said as nicely as possible, considering what theological schlubs Muslims are.
You have to be REALLY careful when you read Church documents.
They often say things in a way that is not obvious until you get into parsing the exact way a thing is said.