Nekogoroshi-hen is fine. If you like Higurashi I don't see any reason to not watch it, its about what you'd expect from a small one-episode special for this series. It follows the general trend of Higurashi's chapters to start relaxed and lighthearted to then turn mysterious and spooky. Some people were a bit confused about the name "Cat Killing Chapter" which I'm pretty sure is a reference to the saying: "curiosity killed the cat." Whether you watch it is completely up to you, I don't feel too strongly about it, watch it if you want to. It has nothing related to anything else in Higurashi,so as long as you've at least watched the first season you'll be fine.