For most other types of questions, we always say that you should make unrelated answers as separate posts so they can be independently voted on. But when it comes to recommendations, the voting is fairly meaningless since there isn't really a "best" or "correct" answer to such questions (Griffiths notwithstanding :-P), and in fact there isn't even much of a basis for judging whether one answer is better than another. So for resource recommendations specifically, posting all the recommendations you have as a single answer is an acceptable option. Posting each book in a separate answer is also acceptable. (Exception: if there is one community-wiki answer that everybody is supposed to edit their recommendations into, just do that.)
Now, if you're making one or more posts of your own, as for what to actually include in them:
All this applies regardless of whether what you want to write is favorable to the resource or not. However, keep in mind that we are collecting resource recommendations, not general criticism. You should only mention resources that you think are worth recommending, and as part of that you should usually have some good things to say about them.
Of course, if you think a resource that someone else has already recommended is bad, you can take steps to point that out, but that's a whole different situation. (TL;DR would be either comment, or edit if it's a wiki post, but make sure you provide a balanced overview of the benefits and problems with the resource.)