In the car chase scene, Samaritan operators are firing at Root's car with a heavy machine gun almost non stop but as soon as she sticks her head out to shoot back, they suddenly stop shooting which gives her a clear chance to shoot back. There is no reason why they should suddenly stop shooting when their target is out there right in front of them.
In the gun battle between Shaw and several Samaritan operators, at first they have her surrounded and they are shooting at her from 3 different directions but when the scene changes, they are only shooting at her from one direction.
Cars do not offer any protection even from low-powered handguns, let alone rifles and machine guns.
When Root fires on the Samaritan operatives with the ".338" during their pursuit of Harold and her, she fires several shots in rapid succession. The weapon she uses is a Desert Tactical Arms Stealth Recon Scout, which is a bolt action/manual rifle, yet Root only cycles the bolt before the first shot.
Root drives Finch away in a car that has been shot through the front by a heavy machine gun; the engine wouldn't run under such circumstances.
When Root shoots at the SUV with Samaritan operatives and it crashes, there is no sign of the machine gun protruding from the roof.
While driving her car, Root notices a sharpshooter on top of a building on the side of the road. It would have been impossible for her to see the sharpshooter from inside her car.
When Greer kidnaps Finch and takes him to a secret location Root and Shaw are able to locate him easily. There is no explanation as to how they were able to locate him when they had lost track of the people who kidnapped Finch.