Although i haven't really played the site
, it seems to be attractive to the players.
For myself I like the Craptcha challenges, which seem to offer incorrectly implemented captchas, which i haven't seen yet on any other site.
Also coming soon is an SQL training series, where you have to construct valid queries and get a desired result set.
Original ideas and fresh wind for the challenge sites, i greatly appreciate the effort the admin is showing!
Carry on with your good work and Happy Challenging!