The watch had a pretty coherent ux flow for a non-touchscreen device, and could be easily used with gloves on without even looking at the watch in some scenarios (e.g. shortcutting to music controls). It later paired some unique animations to make things feel friendly and a bit quirky ( https://www.slashgear.com/pebble-hires-webos-designers-for-u... ).
Also there was a pretty decent hobbyist/maker culture around the watch with the ideas of add-on accessories, etc.
The challenge from a business standpoint mightve been needing to provide vc-backed startup returns without killing the culture that loved the product. I think they were trying to find a way to do a subscription for extra services.