Killzone is doing fine on it's own. The first one was a flop, and perhaps the two portables, but the second and third were overall a success.
Shadow Fall just debuted over 300k, it should do well long term. It's metacritic score is not relevant (see other titles in it's genre that have sold more with similar scores). If you didn't like it, then that's all it is: you didn't like it.
Gaming on: PS4 Pro, Switch, SNES Mini, Wii U, PC (i5-7400, GTX 1060)