It's the only car in the industry that took seriously sustainability. (Sustainable textile, recycled material, end of life reusability and recycling. etc.)
The efficiency is excellent, about 5kwh less per 100km than a tesla. It drives great, it's powerful, fun to drive. I haven't found a i3 owner that didn't like his car yet.
With the range extender it removed range anxiety without add long recharge time on a trip. (granted with more frequent stop)
I bought a used one last week. Maybe it's the honey moon, but it's the best car I have ever own, by far.
The lack of leadership from top executive made the car unpopular, not the car itself. This also led to a lot of employee turnover because the lack of seriousness about the i series.