I saw Singapore Math at Barnes & Noble today, I didn't crack the books at all so can't say how the content is compared to others my kids have tried, but compared to the printed workbooks, my kids have really found the web sites IXL.com and AdaptedMind.com to be very engaging.

My older daughter wants to switch back from IXL to AdaptedMind right now because it's faster to move on to the next tasks, she would get bored repeating the same exercises on IXL. For good or ill, from our experience, it seemed AdaptedMind didn't force you to do as much repetition to "master" a topic and move on.