The UI concepts of Sailfish OS were great, the gestures were simple and intuitive. However, it lacked so many other features. The Android emulator was only compatible with apps for Android 4.4. Although being marketed as secure and privacy-aware, users have no control over apps, as there is no mandatory access control or any other permission system. Remember, this OS has been in development for over five years by now. Also, many parts of the UI stayed closed source, although Jolla promised from the beginning they want to release more open source components. If they wanted contributors, they would have more likely contributed to user-visible stuff like the mail app — not to some lower level middle-ware that is open source.
All of this and some more reasons caused me to finally pull the plug and switch to Android. I wrote about it in lengthy details here: https://raimue.blog/2018/01/09/goodbye-sailfish-os-and-jolla...