Class buffs can no longer be applied to player-controlled pets.
Class buffs and their raid-wide counterparts have been consolidated into a single spell. When the target of the buff is within your party or raid (including yourself), the buff applies to the entire raid. Reagents are no longer required for these abilities.
Weaponskill/Defense no longer is listed in the character window and appears to be removed from the game. Likely all skills are now automatically set to their maximum level based off the player wielding them.
Rebirth cooldown increased to 30 minutes, up from 10 minutes, and is limited to one rez per battle or 30 min (undefined timer).
Starfire range increased to 40 yards, up from 35 yards.
Thorns now lasts 20 seconds, down from 10 minutes; damage increased by 1,400%.
Survival Instincts (druid ability) cooldown increased to 5 minutes, up from 3 minutes. Duration decreased to 12 seconds, down from 20 seconds. Now, instead of adding to health, this ability now grants 60% damage reduction for it's duration.
Blessing of Kings now provides a 5% bonus to stats instead of 10% (and no longer affects Spirit), plus 65 spell resistance at level 80. This makes it identical to the new Mark of the Wild, and in fact the two buffs no longer stack.
Totems are no longer necessary to keep in your bags (if at all). The Air totem quest (level 30) is gone, possibly with the others. Also, this makes the quest to get the combined totem un-completable as you cannot obtain the required item(s).
Though not displayed in the Dungeon Finder Interface Screen, completing your first Random Lich King Heroic Dungeon each day using the Dungeon Finder will award 23 Justice Points, in addition to the 16 Justice Points earned for each boss killed.
Completing a weekly raid quest will be rewarded with 137 Justice Points.
Trainer knowledgebases have been unified worldwide. Classic, Outland and Northrend trainers have learned each other recipes. Accounts without expansions will still be unable to access recipes associated with those expansions.
Herbalism and Mining give XP. The higher level the char is, the lower the received XP will be. This uses rest XP so you will get double XP while you have sufficient rest stored up.
Master Riding is available from Northrend Riding trainers at a cost of 5000, allowing all flying mounts to scale to 310% speed. Characters that already had a 310% speed flying mount pre-4.0.1 are given this skill automatically and free of charge. Note that reputation discounts apply to the trainers in the Northrend starting areas!
Wrathful Gladiator gear, with the exception of shoulders and T2 weapons and the tabard, can be purchased for honour, with no Battleground or Arena rating required (although the tooltip says that it is requires)
You can now activate multiple tracking abilities (Class Trainer, Auctioneer, Mailbox, etc.) including NPC and multiple profession tracking (Track Humanoids, Find Minerals, etc.) simultaneously and the minimap uses appropriate icons to distinguish them from each other; however, it still uses generic yellow dots for Find Minerals, Find Herbs, and Find Fish.
Mounts and companion pets have been moved to the spellbook.
Tooltips of mobs and objects displays quest progression of partymembers when in a party and the quest has been shared.
The character screen now displays the character's talent specialization if one exists.
The background behind the character on the character screen is now greyed.
New Guild UI and cap of 1000 members have been implemented.
If you unsheathe your weapons while dancing, they no longer get re-sheathed.
If you have FPS enabled, it is now displayed on the world map (in a different position than on the main interface)
AddOns can no longer get access to Real Names as the UI merely provides a UI Escape Sequence which is rendered as the correct name when displayed.
The Kalu'ak boat crew now have their voices follow them around when they speak.
Gryphons (the Alliance flight path type) now have their voice remain stationary.
All guards and NPC participants at the Tourney now frequently beat their mounts resulting in much noise.
Consolidate Buffs is now the default setting and has been turned on for you in your preferences. You can turn it back off of course.
A throttle has been added to all public chat channels, limiting players to two messages every few seconds. Players will receive an error message instructing them to wait before spamming sending additional chat in that channel. Other forms of chat (such as Say, Party, Yell, and Guild) remain unchanged.
Links can now be used in all chat channels.
Updated generic portraits are used for Night Elf, Gnome and Troll party/raid members who are out of visual range.
The new raid frame interface allows players to select their role within the raid (the leader/assistants can also set it for them). An option Interface allows players to be grouped together by roles.
The new raid frame interface allows colored markers to be placed on the ground.
When placing a target markers on a target, a line will now be displayed in raid chat indicating who placed which icon on what target.
The "report problem" button is gone from the Help Request window. In its place is an informational page on Account Security. You can no longer report issues to the Game Masters without speaking with one unless you are offline when your ticket reaches the top of the queue.
It is now impossible for Windows 98 & Windows 2000 users to install World of Warcraft (unsupported since 3.0.2, however could still play on them)
It is officially "impossible" to install on Windows 2000, however there is a way to do it unofficially. (This has not been tested on Windows 98!) The game itself isn't incompatible with Windows 2000, just the Launcher requires a small piece of code that Windows 2000 lacks, so loading the game isn't a problem once you get past installation. http://www.techspot.com/vb/topic155005.html has walkthroughs on a few different ways to make it work with Windows 2000. The Wrapper DLL fix is the only one I have tested and succeeded in installing with.
The Launcher will now prevent you from accessing the login screen without an active Internet connection. It can still be accessed by bypassing the Launcher.
Cinematics are no longer included in the digital download. They can still be installed from the CDs/DVDs.