The interface was incredibly fast and intuitive. It was slick and easy to understand but felt modern at the same time. The font felt timeless, it had the best camera app for the time, which was a time where amazing mobile phone cameras were just starting to become a thing (Nokia famously made a 42 megapixel camera for their flagship windows phone and the pics were gorgeous)

The first party software was really fast and stable. They were also some of the first phones I ever used with proper OLED screens

If you ever get a chance to use one it’s worth it even if it’s only for a day. Really changes one’s perspective on what’s possible with mobile devices. IMO nothing has captured that magic again