I've got the Series 2 (first smartwatch I've owned) and it lasts 3 full days.
I'm not wearing it at night and I don't overuse it in the day. I also don't consciously NOT use it, to preserve battery life. Note the double negative. (Maybe I got this wrong; what I meant: I don't make the conscious decision to use my watch very lightly in order to preserve its battery life. If I have to use it, I use it. I don't go out of my way to make the battery last.)
I use Siri a lot, I sometimes take my calls on my Watch (when I am at home or alone), I use it to remote control Apple Music on my iPhone, I receive tons of notifications, I use it to check my work calendar and weather an awful lot, I have lots of apps with background refresh enabled (weather, calendar, emails, etc.), I didn't disable the GPS, it's recording my steps and activity at all time.
Very, very satisfied with the battery life. I thought it would be terrible based on Apple Watch (the old one, not the newer, revised Series 1).