It's entertaining, nothing to write home about.
The acting isn't that great, but certainly not awful and it does show how deranged minds think. Dude walks into a school, commits a heinous act and then starts buddying up with his potential victims like he is some hero. It's pretty natural, most people in a crisis do something they regret later and often will do anything to convince themselves of not being "the bad guy".
Realistically, I don't remember any shooting ever happening like this, it's usually less dramatic and more delusional like the first part of the movie. It would have ended pretty much during or right after people got shot.
I don't know why they made it resemble something like some terrorist, escaped convict or bank robber trying to escape from the police, when Active Shooters usually don't last more than 5 to 10 minutes. Which is hard to make a movie about unless you really go into the psyche or the shooter. There has been only 1 shooting like this (that I know of) in Canada, where Denis Lortie walked into Parliament and shoot a ton of Politicians and René Jalbert talked him down, it's quite amazing and a great show of courage and a clear indication that mental illness is hard to screen for.
In Short: This is less a mass shooter movie than it is a hostage situation movie, it's entertaining and shows how people can have distorted thinking and without help can end ups doing real harm to themselves and others.
The music used is pretty good and adds to the scenes.
