Minecraft wiki entry for Combat_Update, associated text: Changed the layout of the end island pillars and the Ender Dragon boss fight.
Skeleton AI is more difficult.
Sword blocking removed, and several other weapon techniques added.
Tool damage is rebalanced.
Sharpness enchantment nerfed.
Armor strength massively nerfed.
Status effect icons are now visible on the main screen.
Health regeneration is rebalanced.
Fishing is rebalanced.
Brewing stands now require blaze powder.
Enchanted golden apples are no longer craftable.
Maps changed.
Healing system based on saturation.
Attack cooldown on melee tools and weapons.
Loot found in chests generated in the world is rebalanced.
Death in hardcore mode allows the player to continue in spectator mode.
Boats are improved.
Stronghold generation increased to a maximum of 128 strongholds.
Large oak trees generate in forests again.
Increased fire spread while raining.
Glass panes and iron bars have a thin appearance when not connected, as opposed to a crosslike appearance.
Mobs and players now push one another around.
Death message is now displayed on the death screen.
Mob and player heights are slightly modified.
Resource packs can specify models depending on damage value, item state, and hand.
Structure data now comes from /assets/structures.
Loot from mobs, fishing and chests is now determined by loot tables.