I had to chime in here being that I have both an Apple Watch and a Gear S2 3G.
First off, quality control. My Gear S2 has been flawless thus far as far as working right. Build quality is great. My Apple Watch. Lol. I am on my 4th one! All mechanical/electrical failures. It has been crazy! Maybe I have just been unlucky, but really.
Secondly, OS. The Tizen OS interface with the rotating bezel is by far much nicer and intuitive to use in comparison to Apple OS. Of course this is just my opinion, but I think many reviewers would agree. Then there are the apps. I will skip how abysmal the apps were on the Apple Watch with OS 1. Watch OS 2 did improve things there....a bit. I still have many apps that just load and load and load. The apps on my Samsung watch though work quite well. They load fairly quickly. It is still early on, but I expect apps to continue to grow and improve. Of course there are a lot more Apple Watch apps out there, and there always will be, but to be honest, apps on a watch are mostly useless. And then of course most take forever to load anyways on the Apple Watch so I might as well just pull out my phone.
Pricing: my Apple Watch SS with Milanese loop cost around 700$ and the gear S2 3G cost 300$. Hum.
I could go on, but I will leave it here. Of course this is just my experience, so take it for what it is worth.