So far, the problems I've worked on are good. They are very accesible. They are problems that a middle schooler could work on (and solve), but at the same time problems that keeps me--a middling recreational mathematician--challenged. So far there has been no context aside from the context of puzzle solving, so they won't help you determine how the speed of the shadow of a sandbag being dropped from a hot air balloon is changing. Somehow, they've still kept me engaged. :)

The problems are posed (and from the solutions I've read, generally solved) with the lens of a computer programmer. So far I've solved 5 problems without any coding (well, to be fair, I used someone else's code to solve one), but it looks like programming will end up being a requirement for many of the problems. I've skipped one so far that either required some programming, more thinking time, or someone more clever than I. Looking down the list this appears to become more common. Regardless, I find this to be an interesting lens (and maybe a great motivation to bone up on my Java/C/C++/Mathematica/Matlab/Scratch/Perl/Dylan/... skills).

All of the problems (so far, at least) have unique answers. All of these answers (so far) are numbers. While I generally frown on such a focus, I admit that it feels good to put your number in and get a green checkmark (instead of a red x). I also like that answering a problem correctly unlocks a forum where other people have posted solutions (which include both code and explanations).

I also like this response to whether or not you can use google for help.

Making use of the internet to research a problem is to be encouraged as there could be hidden treasures of mathematics to be discovered beneath the surface of many of these problems. However, there is a fine line between researching ideas and using the answer you found on another website. If you photocopy a crossword solution then what have you achieved?All has made me wonder how this or something like this could be used in or outside of school to promote the activity of doing mathematics (or to allow robots to replace teachers). Feel free to wonder with me, or just register and try your hand at some of the problems.