New Boss Battle (as Fionna)
New Model Viewer (with user-made pose)
New Abilities/Upgrades
New Pause Menu (Items/Clothes/Swords/Hints)
New Swords (5 in total)
New Challenges (as Fionna)
Ultimate Tatas Hack
Naked versions (Both in-game and Model Viewer)
New Secret Location
Other Changes:

Revised Targetting system (Camera and gameplay)
New enemy versions (Fruit Witches and Worm)
Hints & Wish Orbs (Accessible through pause menu)
Objectives
Show Controls
Location labels
Puzzles and events reorganized
Save data encryption (Basic encryption)
TV screen update (as Finn)
Removed:

Unity Splash
Tutorial
NPC dialogs for hints
Rope and the puzzle behind it
Minor enemies in Model Viewer
Known Glitches:

The Objective "Visit Jake" doesn't disappear
No audio in Model Viewer
Objective pop-out sometimes doesn't have sound effects
Rotating a bone in "Model Viewer" sometimes give unexpected results
Move/Rotate gizmo in "Model Viewer" sometimes give unexpected results on certain camera angles
Note: The "??? Sword" can be obtained by holding Q and press Right, Up, Down, Down, Down, Up, Right. (While in a level of the game. But due to a glitch, the code doesn't work when you have already obtained the 4-D sword. This will be fixed in the next minor update)