Short version of the release notes can be found below. In-depth explanation post available here.

New Content:
New unit Bowler at Town Hall 10
Inferno Tower level 4 at Town Hall 11
Mortar level 9 at Town Hall 11
Hog Rider level 6 at Town Hall 10
Valkyrie level 5 at Town Hall 10
Goblin level 7 at Town Hall 10

Town Hall 11
Grand Warden Life Aura and Eternal Tome range reduced slightly

Town Hall 10+
Inferno Tower Multi-mode acquires new targets faster
Town Hall 10 and 11 players are less likely to find each other in Multiplayer

Town Hall 9+
All Skeleton hitpoints reduced
Skeletons spawned from Witches no longer trigger traps
Goblin level 6 has been moved to Town Hall 9 (was TH10)
X-Bow levels 2-4 damage increased

Town Hall 8+
Valkyrie damage increased, hitpoints decreased
Valkyrie starts attacking much faster after reaching her target - give her a try!
Wizard Tower levels 5-9 hitpoints increased, greatly increased at later levels
Defending Troops (but not Heroes) flee from Poison Spells if they are standing idle

Town Hall 5+
All Dark Spells brewing time decreased to 10 minutes
All Elixir Spells brewing time decreased to 20 minutes

All levels:
Battle time limit reduced to be 3 minutes per attack once again
Revenge attacks award Star Bonus and League Bonus rewards
New building constructions can no longer be cancelled (upgrades can still be cancelled)

Clan Wars matchmaking has been overhauled - details in the dev blog
War sizes 35v35 and 45v45 have been removed to boost other war sizes
New stat "War win streak" in Clan profile shows how many consecutive Clan War wins a Clan currently has
War Events menu has been redesigned to be much more readable
Number of remaining war attacks can be seen from the Clan War button when outside of the war map
All replays can be viewed directly from My Team/Enemy Team summaries in War Details
"Star button" has been replaced with a bigger "War Details" button on the bottom-right of the war map

Builder Summary: Tap the Builder icon to see all in-progress construction
Tap an entry in the builder summary to select it in the Village
When attacking, army selection bar shows left/right scroll arrows if an undeployed unit or spell is hidden off-screen
Tapping the Loot Cart shows how many resources are inside before collecting
Resource storages have more visual states to indicate more clearly how full or empty they are
Exploding traps indicate their area of effect more clearly in battle
Battles now end automatically if only a Poison Spell is remaining, and no longer end automatically if only an Earthquake Spell is remaining
More replays are stored in the Defense Log and Attack Log, and are available for longer
Army Overview shows time until training/brewing is complete, also accounting for active boosts
Player Profiles unlocked units area reorganized