The thing is, home automation isn't really a new category. Many of us selected SmartThings to begin with because it was using two well-established third-party technologies: Z wave and Zigbee. And home security also isn't new.
Moreover, there have been major introductions into the newest spaces of these categories, most notably Amazon echo, the Phillips hue bridge, and Logitech Harmony home, all three of which have sold millions of units and have very stable reliable systems.
And of course control4 does everything SmartThings does and more, including adding support for Amazon echo, and is stable and reliable. But it's also very expensive, typically 10% of the cost of the house plus an annual fee.
The only revolutionary part of SmartThings is the price. Obviously low price in and of itself doesn't have to mean unreliable. But SmartThings marketing promises a control4 type experience at a relatively tiny price. So far they've been able to deliver the power and flexibility, but not yet the reliability.
As for whether it's trending better – – you can look at either the official status page or the unofficial first bug reports and the number of major outages has been about the same for the last year, usually one a month. And several minor issues.
As far as my personal experience, I got my system in the early fall of 2014. My best experience in terms of the combination of features and reliability was in August 2015. In October and November 2015 reliability fell completely apart, but then there was some improvement until March/April 2016, when it fell apart again. (so much so that the company CEO posted to the forums).
In the past year, my guess would be that there has been statistical backend improvement in terms of the company's ability to service more accounts and more complexity. There have been some additional official device partners added, like Arlo, Ring and iHome. The community-developed Core smartapp has hugely added to the sophistication of rules management for stacked conditionals without requiring that everyone write their own code. And community – created projects like AskAlexa and EchoSistant have added some amazing functionality.
So there have definitely been significant improvements in the last 10 months, but I don't know that there's been a trend towards improvement in system reliability for individual customers. The number of outages is about the same, as is the general flakiness that requires people to pop the batteries on a sensor or run a zwave repair or re-create a rule in order to get things back to working the way they had been the previous week.
For many people, the instability and the time it takes to address it is worth it to get the really amazing flexibility and versatility of the SmartThings system at this low a price. Other people have chosen to move on, either to more expensive systems or to ones which offer much less functionality but have more stability. And still others have chosen just to move the mission critical aspects of their systems, particularly security, to another platform while keeping SmartThings for convenience options.
There's no one right answer. Each person has to decide for themselves what factors are the most important for their household and what they're willing to pay to get them and then find the system or systems which is the best match to their own needs.
Certainly SmartThings has said that improving stability is one of their top company priorities. I definitely hope they succeed in that. But for now, I would evaluate the product based on what it does today, not on any hoped for trend line.