The main gripe I've got with it is that those at the game don't have any idea of what's being looked at. I think the fact they don't want to show it on the big screens in case it's controversial sums up the confidence that must be held by those in charge of the system. Even on the TV it's difficult to understand why things have been given or not given, hiding the VAR person away and not having them talk through their decision seems to add to the controversy to me.
Again it's also inconsistent just like the normal referees anyway. Salah gets a penalty for a slight tug up one end, and their keeper goes unpunished for a blatant push on Barry, where we actually end up with the goal disallowed!
As someone else mentioned, whilst it got decisions correct, I feel it was used incorrectly last night. The officials seemed to be looking for any excuse to use it rather than making calls for themselves and being agreed with/corrected by it.
I've likened it to the system they use in American Football before, where they had to change some of their rules to make them more black and white in terms of what is an offence. Unfortunately there are too many instances of grey-area decisions to make in football for VAR to work properly as it does in other sports, unless the rules are modified to more black and white versions.