My GAE apps and google services just log there automatically. My non-GCP services require a keyfile and couple lines of fairly trivial setup.
I have a single logging console across my entire system with nearly zero effort and expense. It works incredibly well. Doing this in-house is a waste of engineering resources.
Not sure about other use cases such as visualization and triggering events. I assume they have an API or integrations for such things, just haven't needed it as of yet.
Their pricing changed recently, don't remember the details, but I do remember previously that non Google Cloud nodes did incur an additional cost. Free limits are decent, haven't paid yet for personal side stuff. But YMMV, check the pricing page https://cloud.google.com/stackdriver/pricing
After using stack driver, the setting up your whole logging mechanism in AWS atleast is so backward.