I've been using this series of books with my kinder and 3rd grade children. I like that they really teach understanding of math concepts and problem solving. With multiplication and division, I have had to supplement with additional practice.
I liked so much the book and the whole singapore curriculum that I bought to my kindergaten child to. They love it. It makes math very fun. And we do "math experiments" every day with just enough written practice!!
I LOVE the scaffolding and that this book series teaches MATH, and LOTS of MATH. It's NOT full of extraneous garbage that just clutters up pages. I appreciate that ideas are introduced several times, each time fleshing them out a little more. For example, in the first grade year, iterative addition is introduced, and then multiplication, but it isn't really worked with much, it's just that the idea is presented. And again the second year, but this time, there's more in depth, and it's accompanied by skip counting and some drill.
Skills are clearly outlined with simple and straightforward examples and the corresponding workbook assignments are easy to identify.
If I had to criticize something, I'd say that sometimes there's too little practice, but there are other, additional practice books that round it out nicely.