I worked for a fortune 500 company that had been developing their own in house software for 30 years. They decided that they wanted to switch from their traditional waterfall approach, to scrum and agile.
Honestly, the transition went pretty well. Meetings decreased, test coverage went up, feature delivery rate seemed to increase. People were spending more time working on the problem at hand, and less time creating and managing huge requirement documents. There were rough spots. Obviously requirements didn't go away, we just went to a just-in-time model instead of a heavily front loaded model, and sometimes it was difficult to manage just-in-time requirements in a way that gave everyone clear oversight as to what was being implemented (our business rules were extremely complex for regulatory).
One interesting thing I noticed was that every time there was a problem, people would try to add more layers of bureaucracy to "solve" the problem. The hardest part we found was figuring out which ceremonies were useful to stop future problems and which "solutions" were just a reflexive attempt to go back to the way things were before and make things more difficult for everyone.
Honestly, the transition went pretty well. Meetings decreased, test coverage went up, feature delivery rate seemed to increase. People were spending more time working on the problem at hand, and less time creating and managing huge requirement documents. There were rough spots. Obviously requirements didn't go away, we just went to a just-in-time model instead of a heavily front loaded model, and sometimes it was difficult to manage just-in-time requirements in a way that gave everyone clear oversight as to what was being implemented (our business rules were extremely complex for regulatory).
One interesting thing I noticed was that every time there was a problem, people would try to add more layers of bureaucracy to "solve" the problem. The hardest part we found was figuring out which ceremonies were useful to stop future problems and which "solutions" were just a reflexive attempt to go back to the way things were before and make things more difficult for everyone.