The film itself is more intense than scary.
A man gets shocked while interrogated by Dr. Robotnik, and then prepped for "roboticization" (offscreen, we see him getting carried away, however, we do not see the process, it is implied.)
Sonic crashes and bashes every robot dished out. He is not hurt in any way at all during the movie.
Throughout the movie, oppression is a common theme, and after seizing control of Mobius, Robotnik commonly interrogates anyone who has seen Sonic, a.k.a "The Blue Blur".
A few G.U.N soldiers are cornered by robots. Sonic eventually comes and saves them from harm.
The film has a dystopian and apocalyptic kind of tone. Before Central City was taken over 3 months ago, the place was vibrant visually. Now, it is both bleak, visually and physically. May disturb some.
Overall, not that bad of a Sonic film. More disturbing than violent.