Alex Guyot reviewed watchOS 2 for MacStories:
Software defines the Apple Watch as much, if not more so, than the hardware which embodies it. But as well designed and integrated as the first iteration of the Apple Watch’s software (aptly named, though questionably capitalized, watchOS) was, it wasn’t perfect. Some might argue it wasn’t even acceptable. Third-party apps were underpowered and massively handicapped by long load times; when disconnected from its iPhone, the Watch was rendered useless for almost anything except telling the time; and with no Activation Lock, stolen Watches could be reset and resold with ease.
Enter, watchOS 2.
One thing I didn’t notice in Guyot’s review is a comment on overall battery life. When I was running watchOS 1, I’d get home with probably 15-20% life at the end of the day; with watchOS 2, I’m seeing 40-60% left at the end of the day, and I am certainly not using it less.
Don’t miss the footnotes in this review; some of his best observations are buried therein.