Arrow may never be the same after Oliver's startling realization in during the "Kapiushon" episode. Oliver was being held prisoner by his for former friend Adrian, who also goes by the name Prometheus. In order for Oliver to be free, Adrian only asked for one thing -- a confession.
Oliver tried confessing to the fact that he killed Adrian's father, who was a terrible man, but that wasn't enough. In fact no matter what Oliver confessed to Adrian kept telling him it wasn't the one thing he waiting to hear. Adrian said, "I want you to confess to the one thing that you've been afraid to admit to yourself."
After a few flashbacks and some intense coaching from Adrian, Oliver made the realization that he killed the people on his father's list not because it was justice but because, as Oliver said, "I want to and I liked it."
With the revelation out of the bag, Oliver said "It's over for me. I don't want to do this anymore. I'm shutting everything down." Is this the end of Arrow? Probably not.