What does "success" look like when adopting DevOps?

Success for me is when your developers can demonstrate a CI/CD pipeline from code check-in to production that runs without human approvals, without anyone watching it and your IT team is comfortable with this.

There are a few different ways that success manifests in a DevOps transformation. One way is happier employees and less staff burnout. That applies to your developers, certainly, but also operations, security, architects — all of the people working on your product are happier. (This is also a KPI that you can measure using an NPS.)

On the client side, what you can clearly see is that you get happy clients (which you can also measure with an NPS). 

On the company side, success looks like a faster time to market, more value for your money, better efficiency, and better quality in the end, alongside reduced costs. Those are also things you can measure.