Regarding the battery life..
How long are you expecting to be using it every day? Holding your arm up to look at whatever is on the display for an extended amount of time will cause fatigue. It is intended for quick glances at information and some basic interactions. Also, the display is small enough that most would not want to be doing anything serious with it considering there is an iPhone in their pocket or bag that is much easier on the eyes to complete tasks. Most 3rd party apps will likely act as advanced notifications or remotes that are complementary to the iPhone app.
Sleep tracking is also likely to come in the near future. Considering how small the battery is, it will likely be able to be fully charged between 30mins to 1hr. So you can charge it while having breakfast or on a lunch break and enjoy using it for the rest of the day and night.
The beauty ofWatch is that it takes something that people used to only use for time and fashion then goes a huge step further by providing more relevant info to the user, allowing the user to keep in touch with others in new and fun ways, and get the user to be more active and health-conscious. I for one can't wait for April!
I don't get all this whining about the battery life either. So you have to put it on a charger every night. Don't we all do that with our devices already?