What does Chanukah actually celebrate?

Ruminations on the malleable nature of Chanukah here and here. As Paul Greenberg concludes:

There is more than a single theme to this minor but not simple holiday. One can almost trace the ebbs and flows of Jewish history, its yearnings and fulfillments, its wisdom and folly, its holiness and vainglory, by noting which themes of Chanukah have been emphasized when in Jewish history.
So does history say more about the time in which it is written than the time it describes. The message of Chanukah changes from age to age. And the past we choose to remember becomes the truest reflection of any present.