This modpack is focused on Serene Seasons and other mods that integrate well with it. I have tried to keep this modpack small while also still adding enough to make things more interesting than vanilla Minecraft. The main mods I have added to fit with Serene Seasons are:

Upgrade Aquatic, Atmospheric, and Environmental - More biomes and variety of food as well as more varied wildlife.
Farmer's Delight, My Nether's delight, Ender Delight and Fruits Delight- Bigger variety of food to ensure you can always grow something no matter what season it is!
Spice of Life Onion Edition - To reward you for and encourage eating a bigger variety of food.
Tectonic and Cliff Under a Tree (Clifftree) - To revamp terrain generation and make worlds more exciting to explore and also because I'm a sucker for worldgen mods.
Haunted Harvest and Snowy Spirit - Changes villager behaviour in certain seasons and adds special holiday themed food and blocks!
Better Days and Serene Seasons Plus - How much of a Minecraft day is daytime and how much is night now adjusts according to what season it is! Shorter days and longer nights in the winter, longer days and shorter nights in the summer!
Seasonal Integration - A datapack I made specifically for this modpack that ensures all the mods I've added work properly with serene seasons in the intended way.

I have also have a secondary theme which is the world changing around you as you play as opposed to you changing the world with your actions (which you can still do by the way). I have used various different mods to achieve this including:

Enhanced Celestials - To make nighttime more interesting every now and then and create some incentive to avoid skipping the night. I have also made custom lunar events exculsive to this modpack!
Respawning Animals - As animals can now despawn and respawn like monsters you won't find the same animals in the same places all the time! It simulates animals moving around the world and feels more realistic in that sense.
In Control - To adjust mob spawn rates (passive and hostile) according to the season. Passive mobs no longer breed or spawn during non-tropical Winter so plan ahead!
Saplanting - Saplings and various other plants will plant themselves in the ground if dropped as an item, allowing forests to regenerate by themselves after some wood harvesting or forest fires.
Snow Real Magic - Snow builds up on top of various vegetation and flowers properly in Winter like it should!
Dynamic Surroundings - Not only do all biomes have ambient sounds like nether biomes, it also changes according to what season it is and what the weather is doing!
Pillager Caravans - Illagers can sometimes pass through while transporting various goods, do you let them pass by with their ill gotten goods? Or risk your life to get some loot?

If you experience any issues with the modpack please let me know. I'm only one guy so it's impossible for me to catch every issue but I try my best!

Now get and out there and enjoy the seasons!

Tis the Season