I think the problem with the tileset is that it's too dark and gloomy looking. When you think Pre-Historic Era, you normally think lots of green. Tall trees with great hanging vines, rich green moss, mirky brown water, so on. Pretty much like a rainforest.

So, I think you should try and brighten up the grass a bit, and such.

Also a suggestion, for a winter tileset change, rather than just have it snow covered, make it an intense snow biome type situation. To replicate Pre-Historic Ice Ages.

But then again, it's your server. Do whatever the hell you want. I just think changing that up would please a lot of people who are put at odds with the tileset.