In Volume 18 Negan is seen a lot more and his character is given some depth. He's more than just some crazy person with a bat. At times he seems to be reasonable. If he's getting what he wants, anyway. I think he can be very unpredictable though, and he definitely can be violent.
Not too much happened in this volume other than seeing more of Negan, learning about the Saviors and also seeing some new characters. I liked this volume and look forward to continuing this series.