Well, the Cresselia quest was a joke as you said. Though Heatran's quest involved some more walking and exploring, if I remember you even had to go back and return to make him/her appear. But ah well, some more background story would've been nice I guess..Heatran was just "go here, do this, recieve X"
Cresselia was the same.
I mean, hell, they could have made Cresselia's story much more interesting. Rather than conveniently getting the Lunar Wing or whatever it was called, it should have been an Item it held. Meaning you had to chase it down and catch it to save the little boy - which then leads you to Darkrai, who's lurking in the Haunted Mansion. (screw it being event-only)
Come on Gamefreak, at least try.