I posted this review one of my forums, and thought I'd cross post it here. Their website is www.mathusee.com
I love it! They will send you a free demo video if you ask. Once Bob saw the video he was sure this is the way to go. We really really like it, of course we've only used the Primer (kindergarten) level so far.
I do alter the lessons somewhat. After reading How Children Fail I have taken a lot of Holt's suggestions for the Cuisenaire rods and applied them to the Math-U-See blocks. This doesn't change the content of the lessons, just how I present them. I do a bit less instruction and a bit more guided exploration. I also don't have Pauly do much work in the Student book. Instead, I have him work problems with the blocks and write any numbers on a blank piece of paper. He has poor fine motor skills and was getting frustrated with the book.
The order of lessons is quite different. Several lessons back we cover place value -- hundreds, tens and units. Pauly can look at any three digit number and read it correctly. The lesson we are currently working on is "counting to 20." Of course, Pauly can already count to 20 and has for a couple of years, but this lesson is really preparing for carrying in addition. One of MUS's main points is that you can only count from 0 to 9, after that you are counting something else (ie. tens instead of units).
My degree is (sort of) in mathematics and I really enjoy math, and I like this program a lot. I think the blocks and what can be done with them is neat, and I like the emphasis on place value and truly understanding numbers. I think, however, that we MIGHT have been able to get away with only getting Alpha and skipping the Primer level, if we just took the curriculum very slowly. The student book is, at this level, actually incidental to the hands-on lessons.