Timberdoodle does have a lot of fun looking stuff.
DD is 5.5yo, we got book 2. So far I guess she hasn't gotten anything "wrong", so maybe it is too easy, but she doesn't mind that. It is black and white, but DD is more having fun with the ideas of the puzzles themselves, not the pictures in it. It isn't a magical book - it has simple analogies and sequences, etc. DD just likes it and it fits the "critical thinking" category you mentioned.
I am just reading a science text - Building Foundations of Scientific Understanding - that is for K-2. Right now I am in the intro and the author is spending a lot of time talking about how to support thinking and discussion without giving answers and while creating interest. It isn't rocket science either, but it is interesting. One on one a person tends to do some of what the author suggests anyways. There are certain things he has suggested so far - like how to handle different types of questions and suggestions for good leading questions (such as: I wonder how...? and What do you think causes...?) that are natural but when brought to my mind to be more intentional about asking questions that way would very well lead to more critical thinking on the part of my child. Besides the approach being very good, I think the text does seem like a really good one for science, if you are interested in one. It's all about connecting experience with understanding.