Ending started getting stupid *spoilers*
He kills two guys and forgets about the other two? Really? Then he gets the gun from the cop and when the guy grabs him from behind, doesn't just turn and shoot him. That would be a natural reaction anyway. Then the chick crying up a storm when she knew all those guys were bad and she doesn't even try to pick up the gun to help. Just starts whining in the car. Then, they don't even kill the guy but hold him hostage in the house again? Why? Just kill the guy and rape the girl and get over it. No, we gotta torture the guy by inflicting a belly wound on him and leaving his buddy for clean up. Then it get's worse as he's able to find a handcuff key that dropped on the floor behind him! How convenient that he falls where his hands can easily pick it up. Now he's like semiconscious and arrives too late to save his friend from being brutally raped and beaten but somehow has the strength to swing a giant sledge hammer (best part of the movie) and destroy the bad guys knee, get in a fight of fisticuffs and stab the bad guy and smack him once more with the sledge hammer. At least the chick survived.
Watch Paranormal Activity 3 For Free.
http://www.youtube.com/watch?v=pIgZ7gMze7A