Warped Forest
Warped Nylium looks like cyan lichen, and nether sprouts were retextured to contrast more with their surroundings.
The End
End Bricks were given some irregular randomization. Chorus flowers also have a new model, loosely inspired by the Better End mod.
Lush Caves
Not much else to say about this one. Lush caves!
Crops
Bees have biome specific textures and baby textures (requires Optifine). Melon and pumpkin stems have custom models, and wheat grows 1.5 blocks tall. Saplings have 2 growth stages. Double mossy cobblestone slabs also turn into stepping stones.
Butterflies!
Butterflies randomly spawn on flowers! Their wings flap, and there's six different colors to find. Not all flowers have them though, and the butterfly type is unique to each flower.
Crimson Forest
Hoglins were retextured to look a bit more fearsome. Crimson roots also look more threatening with the addition of large thorns.
Spyglass
The inventory model for the spyglass was changed to a 3D model that can be placed in floor item frames as a decorative item. Also candles were given a new model to add a bit of variety to their sizes.
Cactus Creeper
Creepers have biome specific textures! In deserts, they spawn as cactus creepers. (Requires Optifine)
Sunset
At sunrise and sunset, light rays appear in the sky near the horizon for a short period. (Requires Optifine) Inspired by FiftyWalrus' Smooth Operator resource pack.
Survival UI
I tried to give the UI a bit of a backpacking kind of feel. Recipe book is an actual book, and there's chipped wood and little note papers.
Fancy Ice
Ice and packed ice have a subtle border around them now (requires Optifine). Also wooden fences have a custom texture.
Taiga Rain
Rain particles have been reduced for better visibility during showers and storms. Sugar cane also uses Optifine CTM.
Spooky Fortress
Nether Fortresses have been given an upgrade. Nether Brick fences now use a custom fence model and texture. Nether brick blocks also have some ornamental contouring thanks to Optifine CTM.
Shooting Stars!
In flat land biomes, you'll occasionally see animated shooting stars in the sky at night. (Requires Optifine)
Swamp Overhaul
Swamps have updated colors for the grass, sky, and water. Other plants also have custom textures, from curled weeds, to cattail reeds. Vines also appear as spanish moss in this biome. (Requires Optifine)