I haven't played Terraria since before 1.1, how much has changed?
well
everything has been greatly expanded
fishing and stuff
dyes and stuff
there's an alternate corruption
there's now five types of damage
summoner is a new class
there's a snow biome
the jungle has more bees
you can now sacrifice the guide to the wall of flesh
killing that engages hardmode
an anti-corruption fairytale land was introduced
there are mechanical bosses
pirates!
there's more in the jungle after hardmode
the jungle has a hardmode boss after the mech bosses
killing it brings the dungeon into hardmode
spectre armor was introduced then repeatedly nerfed into the ground
^same with vampire knives
killing it opens a temple in the jungle
solar eclipses can happen with horror movie enemies
you can turn the moon into a pumpkin and halloweeny stuff
you can turn the moon into a snowman and christmasy stuff
there's a golem in the jungle temple
you can fish in the ocean and summon fish dukeron
Martians can invade after golem
spoilers:
there are cultists by the dungeon after golem dies
killing cultists makes weird aliens happen
killing the aliens makes space cthulhu happen