Taptic feedback. Diversity in product design. Digital touch. Architecture of Apps.
Those are all unique to Apple's Watch as is pretty much every aspect of the look & feel. You can argue different watches having the same features but Apple's implementation will always be quite unique.
I don't know if diversity in product design is valid for the watch. There was a UI side-by-side with Android Watch UI products at the reveal of the Apple Watch, and they're pretty much identical (save for the top-level app view)
Put aside the UI. There are a couple different case sizes, a few different case materials, a lot of different wrist bands, some special editions, etc. All combined, there are a lot of choices when it comes to the physical appearance of the Apple Watch on your wrist, spanning a huge price range. The Motorola watch comes closest on this score, but it's still a distant second.
Those are all unique to Apple's Watch as is pretty much every aspect of the look & feel. You can argue different watches having the same features but Apple's implementation will always be quite unique.