Watching Scooby-Doo 2: Monsters Unleashed is a bit like being rushed through Six Flags by a parent intent on getting his money's worth. The candy-colored digital imagery looks listlessly and hastily troweled on (no character, computer-generated or otherwise, makes convincing eye contact with anyone else), and head-smackingly obvious tie-in lines like ''How come we can never investigate a Burger King or something?'' test the limits of what merrily expedient selfawareness can excuse. All of this comes as no surprise to anyone who saw the first ''Scooby,'' a good-natured if incoherent attempt to update a 35-year-old Hanna-Barbera junk-TV mainstay. (Then, as now, I reject Sarah Michelle Gellar's Buffyfied Daphne.)
There's nothing overtly better or worse about this sequel, where the series' classic villains are reborn to wreak revenge on those meddling kids. But the ''kids'' look to be pushing 30 now -- an awkward age for theme-park performers.