IMO, Dark Empire isn’t all that bad; its greatest sin is glossing over events which the writer really should’ve went in-depth into.
Its sequels, on the other hand, are rather dire. There was the germ of a good plot in there – Luke’s nascent Jedi Order taking on the last of Palpatine’s Dark Side Elite – but it was overshadowed and ultimately smothered beneath yet another return of Palpatine which ended on a very stupid note.