I love challenge caches and in first instance I thought it were good, to have them back. Some of the new rules make sense (owner has to fulfill the challenge himself, located on listing co-ordinates or with open waypoint, no more trackable challenges). Unfortunately, the chance to create a new icon has been missed. But most important and very disappointing: Some of the new, very restrictive rules mainly destroy most of the fun with challenges. I think, 90% of the challenges, I liked the most or in which I really put an effort, would not be acceptable today:
No more founds per time challenges (visiting 16 German states in one day was one of my best geocaching days ever and visiting 9 countries in 8 days was a great week of geocaching with friends), no more spelling challenges (I don't really need them, but they are easy to check and cause no problems for reviewers, so I do not understand, why they are not allowed any longer), no challenges with reference to cache title or GC number or without checker (for me it was always fun to analyse my finds looking for cool caches for a trivial pursuit challenge or to find postcodes in the GC-number or caches with trees in their name, etc.).
So, only boring new challenges are allowed today. Easily checkable, they become quick grabs for everybody and just another point for the statistics. As a conclusion and in my opinion, in such a restrictive environment the return of challenge caches has not really been necessary.