The Meaning of Life, the Universe, and Everything.
I love the Autumn Forest. It seems nice and neat, with warm colors. I like the yellow-orange-red color of the leaves. A bit moe yellow/orange-ish hue for the grass would be nice. Well I love autumn forests in real life so I would surely love it too in Minecraft.
The Darklands seems interesting too. Even though I'm more interested on it's dark-rocks and lots of flowing lavas aspect (like volcano. I would like volcanic areas in Minecraft. Why hasn't volcanos got added already!?!?)
These biomes are beautiful. I would normally need to see more detail about them before giving support but the images are really well done and I'd honestly love to see these biomes implemented at some point. You have my support but please add more details about what unique properties each of these new biomes will have.