My main gripe being the battery life, which when I first read about it was convinced it was a gross misprint. In fact the current hype that "Apple Watch is so capable you’ll want to wear it all day long, so we made sure we gave it a battery that lasts all day," is a truly remarkable marketing slogan. Imho any watch manufacturer unable to provide at least a 48hr power reserve is nothing more than an insult to the buyer.
Im not a heavy user and tapping the watch all the time.. It's around my wrist from the morning 6.00 to the evening 21.00 and battery shows about the 70% of the capacity left (may include about an hour listening music (AirPods) when exercising and tracking (gps) without phone with me). I always put it back to the charger on every evenings. and it is full charged on mornings. I guess you could get two days battery for it. But I keep the screen at the minimum brightness - it is enough even under the room lighting but don't know if it is enough in sunlight (can't say because I don't remember when was the last time I saw the sun
My current issue with the watch isn't the battery but the lack of customising it and making it more useful than it is now. I wonder, though, if the lack of the ability to customise the watch is due to the battery life - will it run out too quickly then - or is it because apple is just so obsessive to control everything... don't know. Still, you should do more with it. now I just feel that it is missing lots of opportunities to use it efficiently.