As a big fan of the 13 Ghost of Scooby-Doo, I wanted to like this... truly, but I just couldn't. Here's a list:
They ruined Fred's character, saying he was never the scooby gang's leader and making his role a cheerleader. On top of that, making him clueless and stupid.
They ruined Velma's character with her doing practically nothing the entire movie only to pull out solving the mystery out of her ass in the last 2 minutes.
They ruined Vincent's character making him unable to use magic the entire movie without any real explanation.
Scooby, who is the namesake of the series, did very little. Wasn't even involved in capturing the villain.
Flim Flam was barely in it, and only reunited with the other 13 ghost members in the last quarter of the movie.
No scrappy.
And they made the whole 13th ghost pointless and underwhelming.