Features:

A diverse and picturesque world!

Biomes'O Plenty and Oh The Biomes You'll Go and their Addons add beautiful world generation!

Now in your world there will be amazing animals and monsters!

Alex's Mobs adds 53 new creatures.

Unbelievable and dangerous structures will fill your world!

5+ mods add a lot of structures and dungeons!

Better Nether and Better End!

Nether and End is improved now, and it's gonna take a lot of effort to get through them!

Large caves and mines!

3+ mods add extensive systems of caves and mines!

Botania! (before v1.2)

Grow plants, they'll help everywhere!

And many other improvements!

Full Mod List:

Oh The Biomes You'll Go (by AOCAWOL)
YUNG's Better Caves (Forge) (by YUNGNICKYOUNG)
PlayerEx (by clevernucleus)
Inspirations (by KnightMiner)
AmbientSounds 5 (by CreativeMD)
Elytra Slot (Forge) (by TheIllusiveC4)
U Team Core (by HyCraftHD)
Inventory Tweaks Renewed (by godemperordoge)
Enhanced AI (by Insane96MCP)
BetterNether Reforged (by someoneelsewastaken)
Aquaculture 2 (by Shadowclaimer)
Biomes O' Plenty (by Forstride)
Forgiving Void (by BlayTheNinth)
Cosmetic Armor Reworked (by LainMI)
L_Ender 's Cataclysm (by mcl_ender)
Toad Terror (by Cicoda)
Patchouli (by Vazkii)
YUNG's API (Forge) (by YUNGNICKYOUNG)
Sound Filters (by Tmtravlr)
Compat O' Plenty (by tdstress)
Guard Villagers (by almightytallestred)
MrCrayfish's More Furniture Mod (by MrCrayfish)
Dramatic Doors (by FizzWare)
Spartan Weaponry (by ObliviousSpartan)
Pam's HarvestCraft 2 - Food Core (by pamharvestcraft)
Curios API (Forge) (by TheIllusiveC4)
Tidbits - Villagers, Discs, and More! (by BlueDuckYT)
End Remastered (by jack_bagel)
Paragliders (by Tictim)
Divine Missions (by mcrobertx22)
YUNG's Better Mineshafts (Forge) (by YUNGNICKYOUNG)
Repurposed Structures (Forge) (by telepathicgrunt)
Chunk-Pregenerator (by Speiger)
Valhelsia Core (by ValhelsiaTeam)
AstikorCarts [Horse Carts] (by pau101)
Structures Plus II (by Qra5)
Advancement Plaques (by Grend_G)
GeckoLib (by ThanosGecko)
CodeChicken Lib 1.8.+ (by covers1624)
Caelus API (Forge) (by TheIllusiveC4)
Traveler's Index (by idrae_)
Time Core (by Time_Conqueror)
The Abyss II - The Other Side (by y4z0n)
Valhelsia Structures (by ValhelsiaTeam)
Iceberg (by Grend_G)
Mowzie's Mobs (by bobmowzie)
Loot Games (by Time_Conqueror)
AutoRegLib (by Vazkii)
Small Ships (by talhanation)
Moonlight Lib (by MehVahdJukaar)
BetterEnd (Forge) (by Beethoven92)
Callable Horses (by Tschipp)
Somnia Awoken (by Su5eD)
FallingTree (Forge&Fabric) (by RakSrinaNa)
Two Players One Horse (by Beethoven92)
Death Compass [Discontinued] (by Fuzs_)
Alex's Mobs (by sbom_xela)
Mouse Tweaks (by YaLTeR)
Quark (by Vazkii)
Puzzles Lib (by Fuzs_)
Epic Knights: Shields, Armor and Weapons (by magistu_)
MrCrayfish's Furniture Mod (by MrCrayfish)
ToroHealth Damage Indicators (by ToroCraft)
Nef's Medieval decoration (by neoelfe0)
XP Tome (by bl4ckscor3)
Controlling (by Jaredlll08)
MmmMmmMmmMmm (Target Dummy) (by MehVahdJukaar)
Chocolate Fix (by AlcatrazEscapee)
Forbidden and Arcanus (by cesar_zorak)
Antique Atlas (by Hunternif)
Faz's Medieval Gear (by MisterFazCraft)
Iron Chests (by ProgWML6)
RandomPatches (Forge) (by TheRandomLabs)
Inventory HUD+ (by dmitrylovin)
♪ Toad Terror Battle Music ♪ (by my_name_is_krossy)
Library of Exile (by mcrobertx22)
The Endergetic Expansion (by TeamAbnormals)
Goblins & Dungeons (by superlord_9362)
Corpse (by henkelmax)
Stalwart Dungeons (by Furti_Two)
Waystones (by BlayTheNinth)
Just Enough Items (JEI) (by mezz)
CreativeCore (by CreativeMD)
Mantle (by mDiyo)
Citadel (by sbom_xela)
Blueprint (by TeamAbnormals)
Supplementaries (by MehVahdJukaar)
Enigmatic Legacy (by Aizistral)
Farmer's Delight (by vectorwing)
Just Another Rotten Flesh to Leather Mod (by alexdaum1)
Brandon's Core (by brandon3055)
Traveler's Backpack (by Tiviacz1337)
Cloth Config API (Fabric/Forge) (by shedaniel)
Antique Waystones (by HorribleNerd)
InsaneLib (by Insane96MCP)
When Dungeons Arise - Forge! (by Aureljz)
Hwyla (by TehNut)

Advice:

I suggest you download OptiFine for a good job and a comfortable game.

MedievalMagic

Advancement Plaques [Neo/Forge]

Alex's Mobs

AmbientSounds 6

Antique Atlas

Antique Waystones

Aquaculture 2

AstikorCarts [Horse Carts]

AutoRegLib

BetterEnd (Forge)

BetterNether Reforged

Biomes O' Plenty

Blueprint

Brandon's Core

Caelus API

Callable Horses

Chocolate Fix

Chunk-Pregenerator

Citadel

Cloth Config API (Fabric/Forge/NeoForge)

CodeChicken Lib 1.8.+