Minor Plot hole: Marcus is a Terminator with human skin and a heart but he is mainly made out of heavy metal parts. However, he seems to be easily tackled by a teenage Kyle Reese without any problem. Realistically speaking, it should have been like watching a teenager trying to tackle a fridge. Oh and he can also swim for some reason.
Minor Plot hole: A giant Robot the size of a building is able to sneak up on Marcus and Kyle Reese at a gas station without making any noticeable sound.
Minor Plot hole: Before this movie, the Machines launched thousands of nuclear bombs all around the World. No one seems to have any difficulty living in a radioactive environment.
Minor Plot hole: Before this movie, one T-800 (in Terminator 2) was destroyed by molten steel. In this movie, the first T-800 is impervious to molten steel.
Major Plot hole: The Machines lure John Connor to enter Skynet’s main base to save his dad. They then trap him inside the base with the first T-800. Why they didn’t leave more than 1 terminator in the entire base will never be known.
Major Plot hole: The T-800’s method of killing is to toss John Connor across various rooms. He could simply have crushed his head/neck.
Major Plot hole: At the end of the fight, The T-800 impales John Connor with a big metal stick the diameter of a melon. It completely destroys his heart. He is still able to survive until his heart transfusion a couple of hours later.
Super Plot hole: The mythology of time-travel in Terminator’s Universe says that if someone kills your future father: you will also die. Halfway through the movie, Skynet captures Kyle Reese (their top target) and then creates a complex plan to lure John Connor inside a base in order to kill him. They could simply have killed his future father.