When SmartThings works as intended, it is absolutely my favorite home automation system. Unfortunately, since last November I have yet to go 10 days without an impactful SmartThings failure.
The Company Response
The company is well aware of the issues, and has said they are making it their top priority to improve reliability. The company CEO posted to the forums in April, and has been doing weekly updates since then. They have also hired a new chief engineer who was formerly at Amazon and in charge of several of their large projects.
Improvements, but not a reliable system yet
That said, the instability still exists. There have been at least two problems in the last week where things that worked on Monday stopped working on Tuesday, although in the most recent case only customers using a specific feature were affected.
The forum community is great, the staff is great, the company vision is great. But since you asked about the currently available version, it's just not there yet with regards to stability. Top marks for flexibility and versatility, which is why many people stay with it.
Use Cases Vary
So it really comes down to what you want to use it for in its current version. I still use it for convenience cases like getting a notification if the guestroom window is open when it's going to rain. But I have moved anything critical on to other systems.
Some people don't mind a system that need some tinkering every week, even if it's just popping out the batteries on a sensor and putting them back in. Other people want a "set and forget" system. They don't expect things to be perfect, but they do expect the same level of reliable performance as a dishwasher. The Philips Hue Bridge meets that reliability requirement for smart bulbs, and Lutron meets it for smart switches, but few other mass market low cost systems do (and Lutron doesn't work with SmartThings).
I have been doing home automation in phases. (I am quadriparetic, so HA adds a lot to my independence at home, but I also need it to be both stable and reliable. )
There's Real reason to think the future will be better than the past
Originally I had hoped to do my phase II this fall, and had intended to evaluate alternative HA systems this summer, but it's clear that neither SmartThings nor some of the major competitors like HomeKit and Google thread are ready yet. So I'm putting that off right now. In the meantime I'm using bits and pieces from various systems to meet a few major use cases. Right now I'm planning to reevaluate in November, Because it's also clear that several major consumer tech companies are investing significant time and resources in bringing something to market at a much lower price point than the big established HA companies like Control 4 or Crestron.
I give Samsung credit for saying all the right things about home automation, including the needs of those those aging in place or physically disabled, and for investing a lot of money into developing those systems. I am hopeful for the future. But the present is what it is, and right now the maintenance free operating period (MFOP) for SmartThings still seems stuck at about nine days.