How long ago was that? We just switched in January and it's been pretty reliable.
As far as Datadog goes, it's the most team friendly dashboard system we've used. We had a specialty monitoring system for one application stack previously, and no one made custom dashboards there or even just looked at the data. Now we've got custom dashboards out the nose and we're gradually consolidating to a "best of" dashboard for each service.
Datadog may be okay if you're doing really simple stuff and not sending much data. Once you get to scale, you will need a system like Wavefront. Wavefront can take millions of data points per second, query on them super fast, and they don't go down. Every other monitoring system downsamples, or throws away your data after a certain amount of time.
I'm a happy customer of Wavefront. I completely believe that Datadog can handle hundreds of thousands per minute -- especially if most of them are pre-canned, non-custom metrics grabbed by their agent. Hundreds of thousands of metrics/minute is a few thousand a second only. Wavefront does millions of custom metrics per second, which can be sent with different dimensions and tags. That's much harder.
Prometheus can do 800k/s on a single machine. Handling a million per second sounds perfectly plausible to me if you design it properly. The question is more how much it's going to cost you.
Wavefront doesn't publish pricing, but if we take Librato's pricing as a general indication you're talking several million dollars a month.
As far as Datadog goes, it's the most team friendly dashboard system we've used. We had a specialty monitoring system for one application stack previously, and no one made custom dashboards there or even just looked at the data. Now we've got custom dashboards out the nose and we're gradually consolidating to a "best of" dashboard for each service.