Overacting means to act in a theatrical or exaggerated manner, often going beyond what is necessary or natural, usually in a performance. Full definition
The film is saved somewhat from the abyss by Jason Lee, here in his first big role, with his energetic take as Brodie (although he does often overact in a very grating fashion), and some occasional funny lines penned by Kevin Smith that manage to give the film a level of amusement, even if the best lines are delivered without the necessary finesse. (qwipster.net)
The only complaint is that there's a lot of overacting from everyone in the cast, and the motive of the killings isn't exactly clear or sensical. (rottentomatoes.com)
These sequences almost seem ridiculous; not only does Angelina Jolie completely overact as the boy's mother, but Stone's style is reminiscent of countless History Channel documentaries on the same subject. (bucketreviews.com)