People only care about critics, professional or not, when in agreement. If the embargo lifts and we see a flood of 7, 8, 9, or 10s and it becomes certified fresh or whatever then all the sudden Rotten Tomatoes is a reputable source and is jammed down the community's throat in much the same way we're seeing these threads pop up.
As for IMDB, I will say that it shouldn't be an entirely trusted source at this point because it allows anyone to rate and review the film. I know there have been early screenings but I doubt they're all from those who participated. I can literally go there, give it a 10, and regurgitate lore facts to make it seem like I saw the movie but that would be entirely misleading and me being a shit head. Unfortunately, I know a lot of folks who likely would do what I said above or the opposite but that's merely anecdotal.
At this point, all we're seeing from most posters are fringe dick measuring contests from both extremes by those who either love or hate the franchise too much. Underrating a movie by those who wish to see the movie fail because they have an axe to grind with Blizzard and overrating the movie because you have a raging erection for all-things Warcraft are both equally detrimental to the bottom line where the average viewer sits.