This is equivalent to the server monitoring of the New Relic platform, but not the application monitoring side of things, which I think is what most people pay New Relic for.
None of this compares to what New Relic gets you with their deep code introspection. Server monitoring is just an additional gimmick you get with it, mostly because its nice to have all your metrics in one place when you hunt down a problem (there's a CloudWatch forwarder than fetches you all manner of AWS metrics into NR too).
What they are lacking in comparison to running your own NMS (e.g. NetXMS or Zabbix) is making custom views (the Dashboard feature in NR is pretty useless).
During my first couple of hours I encountered a ton of bugs, all of which I reported to SD. Some of them were UI issues — I would edit a chart's settings or an alert, and a minute later my changes had been reverted to the original one. Some of them were monitoring issues, with alerts showing up 45 minutes after the service went down (I was testing with a non-production setup), or not at all, or showing false positives and/or wrong values. And a good deal of SD was not well designed, eg. no monitoring templating.
Also sad to see that plugins cost money; SD comes with very little functionality built in, so you have to rely on plugins.
In general, the whole system seemed incredibly brittle. Not something I would trust a production system to. They have been running SD since 2009, but it feels like an alpha version; not a good sign. (That said, SD's response was very forthcoming.)
I switched to Scout [1], which is not as visually pretty, but works and seems very sturdy. No bugs found so far. Integrates very well with Puppet, easy plugin development in languages like Ruby. Oh, and plugins are free.