Movie studios have no obligation to make movies available to critics before they are screened for the public. I know professional critics don’t like being referred to as part of the “publicity” department for the movies they review – and rightly so – but from the studios perspective, that is precisely what they are. It isn’t free for the studios to give critics advance screenings – they have to rent the theaters and have other costs – so if they feel they aren’t going to get any financial benefit from screening for the critics, why would they do it? It's actually surprising they don't withhold more screenings from critics - blockbusters are criticproof anyway at the box office - but perhaps it's just the realization that in the age of internet, you cannot really escape critic reviews for anything more than a few hours after the first public showing anyway, so they may as well keep the critics happy.
When they don’t screen movies for critics it means one thing – the studio doesn’t have faith in the film. That could be because they know they have a crappy film on their hands, and as I say above, at that point why would they pay to have their film bashed? It could also be, and I think Noah falls into this (much, much rarer category) that they are simply nervous about the reaction – not whether it’s good or bad, but about the content of the film itself. Noah generated a lot of controversy in religious circles for a long time before it screened for anyone. But it was all based on speculation. Once it screens, it’s now based on the movie itself, and has a greater chance of effecting its box office. The studio knew the reviews would be good – which generally, they were – but also knew their target market are not ones who pay attention to critics, so they decided they didn’t matter, and didn’t screen the movie for them. In this case, it wasn't a matter of keeping every critic out - there were quite a few reviews of Noah out days before the film was released, but only selecting a few critics to see it.
I’m not a professional critic, and I never get to see anything in advance, so no, it doesn’t change my judgment – and it shouldn’t change anyone else’s judgment either.