Excellent film up until the silly shootout climax (SPOILERS)

Although I love action-packed climaxes with lots of gunplay, I didn't feel like it fit the tone of the movie at all (or the character) when Tom Noonan pulls out a shotgun and starts firing at people. I thought he was a cunning, creepy serial killer out stalking victims while trying desperately to come off like a normal person. Him resorting to a shooting spree felt like a giant writing cop-out to give us a little more excitement at the end and wrap things up artificially quickly. It's a common issue with these dark thriller movies; the villain seems like they are one step ahead of the cops until they suddenly decide to make an incredibly stupid decision which causes their arrest/demise.