Blue bars are positive reviews. Orange bars are negative reviews.
In the case of Firewatch, you can see a lot of good reviews at launch, then the total volume of reviews taper off, with occasional bumps presumably during sales, Steam front page days, and news/marketing events. Suddenly, on Sept 11th, there’s a flurry of activity, a lot of it negative, that doesn’t match the rest of the timeline. That matches the time when people started review-bombing the game because the dev hit PewDiePie with DMCA takedowns on YouTube after PewDiePie casually tossed out the n-word during a stream.