My Sling subscription just ended, I'll pick it up again for football season.
I had really good luck watching March Madness and Cyclone basketball. Was totally worth the $20 cost to catch the games.
As others have said, it really depends on the device you use. The PC application is horrible - it freezes constantly. The Xbox One app runs okay but doesn't seem to be full HD. The Fire TV app works flawlessly. I've had others in my home that can't believe it's streaming because it looks great and doesn't buffer. iPad app works great, but seems to ask me to sign in almost every time I open it - which is a little annoying.
Sounds like they're developing Chromecast support (should be out soon).
Overall, I think if they can patch up the apps on some of the devices and continue to keep the cost low, it's totally worth it in my house just to watch the Cyclones. Added bonus is during the summer I can cancel it right on the website. No phone calls, no contract, no bills during the months ISU doesn't play.