Sometimes a change in tone from the previous season to the next one can be a good thing for a series. This depends on the show in question. The writers want to take a different direction on where the plot is going and change the atmosphere. As long as they keep adding new elements to the story that doesn’t detract from what makes it suitable, that can be a welcoming change. Just don’t assume everyone will be 100% on board with it. The 2nd season of Sidonia no Kishi can be classified under this predicament.