The Series 1 was more or less an experiment. Basically, I already knew (from using fitness trackers) that notifications on my wrist would be useful... so I wanted to see how the Apple Watch held up (which was one big issue with fitness trackers). It's still going strong after three years, which was the arbitrary durability threshold I'd set.
I've been pleasantly surprised at how well it's held up after three years - both the physical device and, especially, the battery.