is kali linux good?

Kali Linux is like "the ready hacking machine" it's simply a Linux distribution were a lot of tools for penetration testing, exploitation are already installed. If you wanted, you could install them with any other linux distribution.

But your question is sounding kinda "newbie", you can't tell if Kali is "good" or "bad... It depends on what you want to do with it, or you can do with it.