The list below is a compilation of undocumented 2.4 changes that I lifted from wowwiki. I have not yet verified them on the live realms.
The ones that excite me are the new PVP mounts--fear my armored Chocobo--and the new inn music--Blizzard's music is always awesome.
General
Dwarf male shoulderpads have decreased in size, and weapons have increased in size.
Players in Thunder Bluff are no longer auto-dismounted if they travel through buildings to other parts of the city. Druids won't lose their Travel Form.
Quest
Many more Nethermine Ravagers have been added to the Netherwing Mines.
Mage
The absorb values of Ice Barrier have been increased.
Druid
Druids that were in Moonkin Form or Tree of Life Form will now be able to auto-shift out to mount up.
Alchemy
Four new Alchemy Stones added, all need the previous [Alchemist's Stone]
[Assassin's Alchemist Stone] confers +108 attack power plus increases effect of healing and mana potions by 40%
[Guardian's Alchemist Stone] confers +54 defense rating plus increases effect of healing and mana potions by 40%
[Sorcerer's Alchemist Stone] confers +63 damage and healing spells plus increases effect of healing and mana potions by 40%
[Redeemer's Alchemist Stone] confers +119 Healing or +40 damage plus increases effect of healing and mana potions by 40%
Items
Items intended for Retribution paladins have been rebalanced. Spell damage has been replaced with stats such as critical strike, haste, and strength on Season 1 and 2, Tier 4 through Tier 6, and other miscellaneous Retribution gear. Season 3 was already changed in patch. 2.3.
Stats of [Shifting Tanzanite] changed from +5 Strength +4 Agility to +5 Agility and +6 Stamina.
The PvP mounts [Swift Warstrider] and [Reins of the Black War Elekk] have been added to the game.
Sound
Inn music added for tauren and orcs inns.
User Interface
Tutorial hints (after clicking on the yellow exclamation mark at the bottom of the screen) are now displayed in the center instead of at the bottom.
Separate options added to display names of pets, companions, or creations for friendly or hostile units.
Bug fixes
The Falthrien Academy is now correctly displayed as a subzone of Eversong Woods, not as a zone (which has a bigger fade text on entering).
Some mounts (like the epic Hawkstrider) now make a sound, when standing still and pressing the space bar. There has been an animation.
Wind Rider Master Urda, in Hammerfall, is now standing on her platform instead of under it.
