We use Features as user stories that get individually worked within a release (development iteration). However, almost all of our Features roll up to Epics (which then roll up to Initiatives). The current format doesn't allow for the organization of Epics as a part of a hierarchy very well, because:
Epics cannot be created without being defined to a Release, which forces me to have to create bogus releases just to group epics.
When Epics are finally taken into development, they usually span multiple releases. Since Epics are labeled to only one release, the Features board displayed as Epics does not allow for all of the Epics being worked at any given time to display within a release; it only appears on the release to which it is assigned.