I've subscribed to Sling TV for about a year, since it became available in early 2015. It's been a bumpy ride, with technical problems and customer service issues, but for the most part I'm glad that I had it. Now, though, I've decided that it's not worth the monthly subscription fee to me.
When I first subscribed in early 2015, the technical problems with Sling TV were legion. Sometimes I couldn't connect at all. Other times shows would stutter, or stop playing in the middle. The Fire TV app interface was terrible. I stuck it out, though, in large part because the baseball season was coming up and I knew there would be plenty of games on ESPN. By mid-summer, the technical problems were significantly reduced. There are still occasional problems, but now they're the exception, not the rule.
I also had some customer service troubles. I originally signed up with a two-week free trial offer that Sling TV was running through Amazon.com. When I decided to go ahead and subscribe after the trial, I kept getting errors. I had to call customer service several times, and eventually just close the account completely and set up a new one through Sling TV directly (with no Amazon involvement). It was just as difficult to add HBO to my subscription a few months later (at Game of Thrones time, of course). Again, things did improve. By the time I cancelled the HBO portion around the end of June, I was able to do so via the website without major difficulty.
So why am I dropping Sling TV now, if things are better? Mostly because I just don't use it enough to be worth the monthly fee. The only channels I really watch are for sports (EPSN, sometimes TBS). I watch a whole lot of video, as anyone reading this blog already knows, but the vast majority is either over-the-air channels or streaming services. If Sling TV had some other sports content, like FOX Sports (mainly for hockey) or the MLB/NFL/NHL Networks, then I might feel differently.
Another reason for dropping the subscription is the lack of DVR functions for the channels that I watch. There's no recording of shows to watch later, or even short-duration pause/rewind of live TV. Twenty years ago, that would have been fine, but now? That sort of functionality is pretty much the standard these days. I rarely watch any non-sports event live, and I make heavy use of pause/fast-forward/rewind even during live events. Lack of those features lowers the value of Sling TV significantly for me.
I might think about coming back around next fall, when football comes back on, since there's a whole lot of college football that's exclusive to ESPN, as well as Monday Night Football games. But until then, I have other sources for my hockey and baseball sports fix (mainly Internet radio) and nothing else that's worth paying a monthly subscription.