As is most often the case, seasons in MMO's are purely window dressing. They don't tend to change anything physical, and instead act as events, or are purely cosmetic. Crowfall wants to change all that, not only with the game-world changing around players, but seasons also bringing their own benefits (such as higher attributes for gathering in Spring, but less in Winter). It's a hefty post by Thomas Blair, but sounds brilliant. Full details here.