I don't trust user reviews for a game like that, most of them probably haven't played it. I think it's just people angry about the DLC.
Regardless, it has set the trajectory for sales fairly well in the past, no? The game just launched and it's tracking below dozens of other games, including older releases. This is not a very common occurrence for great sellers, from what I recall.
Angry or not, people don't seem to be swallowing Evolve. We'll see how it does next month, but I expect it to be a pretty big sales disappointment for all parties involved.