I think there are three things that are very important for a good smartphone
First is ease of use from the OS. A fancy keyboard and fast 3G connections mean nothing if someone has to go through 5 different menus just to change the sound profile.
Second is hardware quality. A smartphone is something someone will rely on and it cant lose a button or start shutting down by itself.
Third is connectivity. A smartphone was designed to be used anywhere at anytime. Whether its global 3G or Wi-Fi, it must be able to provide easy access that the smartphone owner requires