Thing is if reviews didn't effect box office then why did a film like Fantastic four flop? it only made $168.0 million so not many people see it, was it the trailers not being good? would it still have made that much even if the reviews had been great? there is clearly something that put people off and i doubt it was the 2 previous films
Reviews obviously have some effect but people do not necessarily rush to RT to see a collection of all the reviews.
They might hear a review on a TV show (we have a film reviews show on television here in the UK), read a single review in whatever newspaper they see/buy, or see the review rating on a cinema website (in the UK, audiences on the Odeon cinemas site can give a review of a movie and it then gets a score; before release, it's given a 'buzz' rating).
And there are other factors - marketing, popularity/reputation of the franchise, content of the film itself, etc.
So what went wrong with X-Men: Apocalypse? Well, obviously, the content of the film (the grandiose villain, the re-treading of things already seen, the disaster movie plot) led to some poor reviews as well as being off-putting for a proportion of the public. The film needed a lot more zip and substance. Things that weren't developed should have been, things that were front and centre should not have been.
While it might serve to thematically wrap up the Magneto/Mystique/Xavier arcs and show the redemption of Xavier as he finally creates his family of X-Men, that is (as a non-geek friend said to me on FB) somewhat indulgent for a summer blockbuster.
I'll still enjoy watching this trilogy, but I can see where it didn't resonate with a lot of the general audience.