I use Google Analytics for many sites and I use it pretty much every day. I’m not the world’s best user but I’m reasonably competent. I speak from some experience.
And here’s the single thing that would make the product waaay better: Annotations on the activity timeline.
Because you make changes on an ongoing basis to the reporting. So how about show those changes in a nice little annotation on the timeline. Where possible, make the annotations automatically added, especially if the changes are system defined or parameters.
Then let users add notes to the annotations. Create a logbook of those annotations so you can see the change you made over time in stream outside of the timeline. But also make them available in the timeline, because that’s where you want to see them, because that’s where you see the correlative results of the changes.