I like challenge caches and therefore I was happy to see them coming back. However, it was quite disappointing to see all those restrictions that are in place now and which would prevent some of the most interesting and creative challenges I did in the past from being published now.
Some of the guidlines obviously make sense and I can see the point of some others (e.g. the necessity to have a checker, although it was also fun to search the archives to see whether I qualified or not, cf. the wonderful challenge GC515W1 "In een klein stationneke... (https://www.coord.info/GC515W1). However, others limit the possibilities much too much. Why, for example, should you not be able to use other geographical critera other than countries, states and counties as long as checker can be created for this? If I understand it correctly this would exclude interesting challenges e.g. based on topographic maps (cf. GC6G2MT: Belgium Topo50 Challenge: https://www.coord.info/GC6G2MT) or 360° challenges. Or why on earth should it not be possible to use cache titles, GC-codes etc.??? Or why not percentages of found caches in an area? Also the timing requirements are much too restrictive. After all, as with all other caches, nobody forces you to find a specific challenge which might be too difficult, but for some of us, who have completed most of the standard statistical stuff, those challenges were a nice way to set yourself a difficult goal.
So, overall, I am happy that they are back, but very disappointed about the stupid restrictions on them. By the way, I would prefer if there were a special cache type for challenges.