Main mods:
Tetra
Twilight Forest
Minecraft Comes Alive Reborn
Origins
RPG Hud
Ice and Fire
Tough as Nails
When dungeons arise
Wyrmroost
Most of the side mods are/add:
Libraries
Mobs
Menus
Items
Village(er) changes
The main New features include
Dragons that aren't the ender dragon both peaceful and harmful with the most common one shooting fire out of its mouth and the the rarest probably also shooting fire out of its mouth
You can form a party by going into the inventory menu (I have no friends)
You can change the material of certain parts of certain items as well as change those parts or completely remove them
You could slowly go into a decent of madness purely out of loneliness after accounting endless villages filled with either farlanders or no one at all unless ur on multiplayer with someone else (I experienced this)
Choose a race and gain great ablitities with the the "but" being drawbacks like being born in the nether but not being able to touch water or being seaborn and cant touch fire (that would make an interesting romance)
Fight many new bosses one of which might be in your basement (I have one in mine)