SmartThings is a very versatile and powerful system, but as you’ve noticed, it’s not particularly stable.
Since November 2015, I’ve yet to go more than 10 days without the system requiring some kind of hands on maintenance. ( and I use almost no custom code, these are just standard features.) A lot of times that maintenance just needs something really simple like popping a battery in a sensor or opening the app and saving it again, so some people barely notice the glitches. However, I’m quadriparetic and I have to pay someone else to do even the simple level of maintenance, so I notice it a lot. 
For the last eight months, there’s been a major outage (big enough to make it to the official status page) in every month except January. Some of these get resolved in a few hours, some take longer.
There are also a lot of problems that only affect some people and don’t get put on the status page, although you can see them on the first bug reports page in the community – created wiki:
http://thingsthataresmart.wiki/index.php?title=Bug:_First_Reports
So it’s definitely not a “set and forget” system by any means. On the other hand, people do have it doing some pretty amazing things. 
So it all comes down to your own needs and Preferences, and whether you’re willing to have a fairly high maintenance system.
There are also people who just set it up for a very simple monitoring and may not notice even the major outages because they’re waiting for the system to tell them that something happened. So the whole system could go off-line for several hours, and they might not even know it. Where someone who had the system set up to operate motion sensor triggered lighting would notice problems immediately. Both very simple set ups using official features, but they might report very different experiences.
There are a lot of alternatives you can look at in the low-end price range, but each of them have their own pluses and minuses. Because of my situation I require a MFOP (maintenance free operating period) of at least six months and preferably 12 for critical use cases. So I have had to move the essential automation off of SmartThings for now, until their reliability improves. I do still use it for convenience notification cases, like getting a notification if the guestroom window is left open, the guest is away from the house, and rain is expected. SmartThings just does those better than any of the competition, and if we miss a notification it’s not a disaster.
I do get at least a six-month MFOP from a number of other systems, including the Phillips hue bridge, Lutron lights, Logitech Harmony, Naran Prota, Amazon echo, Apple HomeKit. But each of these is a much more limited system and features than SmartThings. Still, it means I can meet my minimum needs.
If I had the money, I’d get a control4 system. It does everything SmartThings does and more and is very reliable. But you’re looking at costs of 20 or $30,000 for a minimum system, and typically around 10% of the value of the home plus an annual maintenance fee. It’s just way outside my budget.
So for now, I get along with a mix of different systems, including SmartThings, Covering different use cases, and I keep an eye out for anything new. So I do you share your frustration, but my own solution was just to find better reliability options elsewhere for the use cases that needed that. But there isn’t any one system available in my budget that I can go all in on yet.