This modpack revamps Vanilla structures so it's not boring to visit known structures, and adds some new with customized more difficult mobs. - mods: YUNG's (several his mods), Grand Capitals, Dungeons Enhanced, When Dungeons Arise!

Overworld generation is overhauled by which Your adventure isn't that repetetive. - Terralith, Oh The Biomes We've Gone, Alex's Mobs

Nether is enlarged also with new structures and new boss to fight with. - Amplified Nether, Stalwart Dungeons, Netherific, YUNG's Better Nether Fortress, Nether's Exotism

End dimention is delayed in progression as you need to collect 12 DIFFERENT eyes to activate End portal, as well as revamped main island. - End Remastered, YUNG's Better End Island
There are also mods for End structures and new mobs. - Better End Cities, Stalwart Dungeons, Medieval Buildings [End Edition]

In addition to all of this there is new dimmention from mod "Distant Worlds"

BUILDING got some mods for many new blocks and even customizable ones with a hammer! - Chipped, Handcrafted, Building But Better, Macaw's - (several mods: for doors, trapdoors, fences and windows)

Next there are MANY QoL mods and the best are:

Better Mob Grieffing Control - Enderman can't pick up blocks, configurable Creeeper and Ghast explosion consequences
Better Than Mending - can crouch+RMB to repair mending items from xp bar
Combat Nouveau - changes to combat mechanics for the better (check mod description for more)
Corpse - dying does not scatter Your items anymore! Instead in the place of death Your corpse is created which is invincible (to lava and void also!) so you would never loose Your items, but still need to retrive them
Instant Nether travel - :)
Just Enough Items - in inventory list of all the items in game with recipes
Lootr - so no one steals Your loot!
Quark - for list of features check mod page here
Quick Right-Click - now you can hold Crafting in Your hand and RMB in the air to open it without placing! (works also with shulkers, ender chests and stone cutters)
RESPONSIVE SHIELDS - NO MORE MISSED SHIELD BLOCKS (as for late shield activation causes to take a hit from an arrow with shield up - no more!)
Simple Backups - self-explanatory (default 15min interval, configurable)
Sophisticated Backpacks - Expandable backpacks with upgrades such as: auto pickup, auto feed, auto smelt, auto compact and more!
Trade Cycling - keybind for cycling villager trades without breaking the workstation! (default "C")
Xaero's World and Mini map - tracking Your whole generated chunks as one image (keybind "M")

And many more QoL mods which you stumble upon just playing for comfortable experience ;)

Also as they are smaller mods, I'm mentioning them at the end here:
Construction wand lets you build many blocks at once
FTB Ultimine adds keybing for mining several the same blocks at once
Zoom ;P
Artifacts adds some interesting trinkets to equip which give you some neat helpfull effects
Elytra slot for wearing elytra and armor at the same time as well as Customisable Elytra which allows for dye or banners on elytra
Cosmetic Armor allows wearing second "disabled" set of armor which is only for looks
Farmer's Delight adds many plants and recipes for different new foods
Doggy Tallents Next greatly expands Dog usefulness by letting you train Your dog in different ways and adds many skins for them

Build N' Explore