I own the Gear S2. I've also owned the Apple Watch (S0) and the Moto 360 2nd gen. The interface on the S2 with the rotating bezel works really well. It is the only time I really felt like my smartwatch was an actual watch and not just a "device" strapped to my wrist. The cellular functionality was also handy in a pinch, as it offered some communication utility if I left my phone at home.

That being said, I don't think I'll get the Gear S3. The biggest problem is that while the S2 works great for displaying notifications, the lack of phone apps makes it difficult to take any action on most of them without switching to your phone. On top of that, I found it extremely difficult to get text into the watch to do things like respond to texts with anything other than a pre-selected message template. The T-9 keyboard was awkward and S Voice didn't work well at all (in part, I'm sure, to the quality of the microphone embedded in the watch).

I don't think smartwatches will be much more than notification mirrors until the ability to quickly input text gets better, probably through improved voice dictation.

One other thing about the S3: I really don't understand their choice to offer cellular connectivity only one the Frontier model. That feature is one of the main things that would attract me to the device, but I don't like the styling on the frontier.