Interesting premise but poorly executed.
The main flaw of Trap was the lack of anything deeply interesting happening to keep the audience hooked. Sure, the story is interesting; local and national police trap a suspected serial killer in a stadium using a Billie Eilish-esque pop concert as the cover story. Could be really clever.
Unfortunately, although the tension could have been off the chart, the action, the dialogue and the acting choices meant I wasn't invested enough in the major players. Hartnett made some bizarre acting choices for the main antagonist; I think he was trying to play 'creepy everyday suburban American family man' but it came across as awkward and over-acted.
(The whole conversation about how he and his daughter should check out the underground stage area was just really jarring).
There wasn't enough of a dive into his psyche as to why he was doing what he was doing. Sometimes not knowing is an excellent plot device, but this time around it didn't work. Some flashbacks on the why might have worked well. Who was he? Then the audience might have cared more.
M. Night. Shyamalan has churned out some A grade stories in the past but this should sit quite low down on his repertoire.