The Problem of Pain will discuss Genesis in allegorical terms, which is something that some posters on this board take an issue with. Also it will briefly touch on topics such as the relationship of possible space aliens with God, and it'll spend a chapter discussing the possibility of the salvation of animals. I don't know of these are big problems to you, but I've seen posters object to them before.
And Mere Christianity has been criticized as a sneaky promotion of Ulster-style Protestantism, which is, again, something certain posters on board may have a problem with.