Symbian was one really good OS for the pre-iOS world. A basic S60 button-phone was capable of multitasking, copy-paste, profiles (which Android and iOS still lack) and could even pull off some decent graphics in games that weren't seen till years later on iPhone/Android devices. I even remember writing an app to SSH into my computer in the rather awful implementation of C++ it supported. But it transitioned to touch interfaces poorly, at least initially. The first few versions of S60v5 for the Nokia 5800 were horrid, with basic things such as drag to scroll unimplemented. It did improve considerably over time (by late 2011-2012), but by then the market had moved on.

Also, it was a great OS for tinkerers because it wasn't hard to gain access to the OS files and play around with stuff, install sis and jar files, modify signatures (alright, that's a bit shady but I was ten, give me a break) and whatnot, but I imagine the lack of a central app store until much later did the platform no good either, because apps were slightly hard to find for a general user, and carriers (where I lived) often scammed users by offering free jar apps picked from the web on their portals for absurd amount of money.