I watched "Scooby-Doo! Stage Fright" together with my 7 year old son as part of a Scooby-Doo animated movie marathon. And I must conclude that "Scooby-Doo! Stage Fright" is hardly among the best of the animated movies in the franchise.
With that being said, I am not saying that it is a bad movie. Far from it. It is, however, just similar to 90% of all other animated Scooby-Doo movies. And once you have seen one, you have essentially seen them all. Because they follow the same blueprint and doesn't stray from the generic build-up and Construction one bit. So take it for what it is, for better or worse.
The story is adequate, but it does suffer from being predictable and following the How-To-Make-A-Scooby-Doo-Adventure step by step. Certainly there is familiarity in that approach and the audience is familiar with the concept, but wouldn't it be nice for a change of pace and approach for once? With this animated movie sort of poking fun at the talent shows that constantly show on the TV screens, it does have some appeal. However, while it certainly was watchable and entertaining enough, it just was too much of a repeat of previous movies.
The voice cast in "Scooby-Doo! Stage Fright" is great, as it always is in the Hanna-Barbera cartoons. And it is always a delight to have Mindy Cohn, Grey DeLisle, Matthew Lillard and Frank Welker return to do the voices for Velma, Daphne, Shaggy and Scooby. Furthermore, Vivica A. Fox also gives voice to a character in this particular animated movie.
All in all, "Scooby-Doo! Stage Fright" is just your average, run-of-the-mill animated movie in the franchise. It is enjoyable if you are content with watching the animated movies of the Scooby-Doo franchise as they are and doesn't need change of scenery.