"The Reeve's Tale" starts out trying to be a comedy. All the signs of comedy are there: a miller who regularly cheats his customers, two buddies on a road trip, a night spent all together in close quarters that culminates in several cases of mistaken identity… Yet somewhere along the way, "The Reeve's Tale" becomes very, very dark. It's hard to find the humor in what we might call Aleyn's rape of Symkyn's daughter, or the brutal beating Symkyn receives.
Nevertheless, the tale continues to attempt to make us laugh, parodying the genre of the "dawn song," the address with which newly-coupled lovers say farewell after a night of passion, in Malyne's goodbye to Aleyn; or trying to milk the humor out of Symkyn's wife's confusion of her husband's bald head with the white cap of a clerk. It's possible to read all this as comedic. On the other hand, we might read it as evidence of the narrator's pleasure in the punishment Symkyn receives.
Defining "The Reeve's Tale" as a "family drama" might make more sense, especially given the long discussion of Symkyn's wife's family ties and Malyne's potential inheritance. Although the conflict in the tale is at first limited to the miller and the two clerks, the whole family gets drawn into it in the end, justifying a label for "The Reeve's Tale" as a family drama. In fact, "The Reeve's Tale" might even be making a point about how the "sins of the father" rebound upon his whole family when all is said and done.