For the first 2 days my battery was draining much faster - hitting power reserve mode before bed after a workout. Now battery life is back to where it was in OS 3, and if anything I think performance is better. The new dock using the Digital Crown feels much faster to me, and there are lots of small improvements I like, such as automatically showing the now playing screen if I start music from my phone. I was expecting to upgrade the watch this year but think I will stick with S0 for another 12 months.