I don't know how many of you are Rugby League fans, but the video ref has been used in that sport for at least 20 years (I can still recall a controversial call in the 1999 Grand Final). Probably 3 or 4 times every weekend, you look at the big screen in the stadium, or your tv screen at home, and wonder just how an experienced referee could possibly have come to a decision, and that is excluding the marginal decisions where it can go either way. Every weekend over the course of 6 games, there are 3 or 4 absolute howlers.
For VAR to work in football, it should only be used in black and white cases e.g. was the ball over the line, was it in the area, was the player standing in an offside position (using those blue and red lines across the screen) ? Anything which requires an opinion, such as judging a player's intent, should be left to the refs and asst refs on the field of play.