For my purposes, Sling TV has one big drawback. ESPN is on Sling Orange, and that plan has a single stream. That means only one person in the family can watch a stream at a time. If someone in the living room is watching Sling TV, no other TV (Roku, Chromecast, Fire TV, Apple TV, etc.) can watch Sling TV. The Sling Blue plan offers three simultaneous streams, but that plan doesn't include ESPN, which has most of the college games.
For other purposes, such as regular live streaming usage -- not how I use it, but how many do -- the problem is that there are no local channels. That's not an issue for me, as I have an antenna, and an Air TV device that integrates the live TV (and DVR) into the Sling TV app. But, for those that don't have an antenna, and where an antenna isn't feasible, Sling TV misses a large part of the content people want.
Now, I don't blame Sling TV for forgoing local channels, since the broadcast fees they would have to pay -- and that the other more expensive live streaming services pay -- would mean higher costs to Sling, and higher prices for their product.
It's the same way with the single stream. ESPN costs a lot of money for Sling to carry. That's why they have two plans. Sling Blue doesn't have the six Disney owned channels, including ESPN, that are on the Sling Orange package, but has more channel 17 other channels, giving it 11 more channels net. Sling Blue also has three simultaneous streams, as opposed to the single stream Sling Orange has.
Those are the main problems I see with Sling TV, but there's one other that some people have. That's the number of channels Sling TV offers. Cheaper services, such as Philo, carry more channels. Of course, more expensive ones carry more channels too. But the selection of channels Sling TV carries is actually fine, as far as I'm concerned.
While there are some things about Sling TV that I don't like, overall it's still my go-to live streaming service. It could be better, but the tradeoff is something I'm okay with. Sling TV is a good part of my Streaming Life. Not perfect, but close enough.