I have the Gear VR, and absolutely love it! Everyone I've showed it to (who hasn't experienced VR before) is also amazed at just how well it works.
In terms of performance, it's honestly quite good despite being powered by a phone. While you can't lean forward and back, basic head-tracking works as well as you need it, with virtually imperceptible lag - important for those who tend to suffer from motion sickness). Graphics-wise, it's pretty good, though there's definitely some room for improvement.
The Gear VR does have a lower field of view than its PC counterparts, but it is noticeably better than Google Cardboard. Once you are enjoying an experience/app however, you start to not pay attention to this as much (similar to the resolution).
The biggest issue with the Gear is dealing with heat. Running VR content on these phones tends to generate a fair bit of heat, and can eventually prompt a warning to let your phone cool down. People have done mods to add a fan to the unit, but a much more simple solution is to use some gel packs such as this:
http://www.amazon.com/Reusable-Packs...UvrUvbUpU47543
Overall though, I'd definitely recommend getting one if you have a compatible phone. For $100 it's an awesome way to experience VR, and help decide whether to invest in a PC-based setup for more immersion and capabilities.