Why does some software gather rave reviews while functionally equivalent software never takes off?
Because of a relentless focus on good user interface, exemplified in their effort on eliminating “paper cuts”.
A “paper cut” is a little interaction that is in some way annoying or not quite right. It can be just a superfluous click or an unintelligent default. These kinds of annoyances get pushed back in the development schedule in favor of “more important” things and tend to pile up, unfixed.
Do you have similar low-hanging fruit in your applications? Sometimes fixing a little daily annoyance will get you more love from the users than implementing the next feature.