My Take
This site has some great games for math practice, students really enjoy time on math playground. I like that there are a wide variety of games to choose from, something for every interest, there are also different game "themes" like logic, basic facts, etc...There are lots of ads so it's a little overwhelming at first, but students seem to adjust to the page quickly (more quickly than my tired eyes- LOL). As an aside, it's also a great site to discuss digital citizenship and how sites use advertisers to sponsor them so they can provide free service.
How I Use It
I give my students time on math playground as part of our daily math, it's a wonderful site to simply practice and students are always on task and engaged. I also encourage children to use it at home for practice, no one ever complains about that math homework :). I also use the "thinking blocks" one for struggling students, as it offers a visual representation of the math (abacus and visual models) this has been a great help for older students (gr 4 and up) who don't want to be seen using manipulatives but still require the support. Overall a really fun site that is engaging and movtivating for students, I never worry that they are off task!