-Gameplay- Gameplay has largely been stripped down to be a shell of its former self. This trimming has been going on for several expansions, but now it's even worse. Classes only have so many buttons which has resulted in very little skill involved in PvE (even PvP is a faceroll for most melee, lacking any sort of depth and decision-making as it's pretty clear what buttons to press in any given situation) and it's become more of a gear check. This expansion gave zero new abilities to classes, only took them away.
Update: The reason for less experience from gathering is due to how Blizzard revamped professions and broke them down by expansion. In order to get full exp from gathering you'll simply need to find a profession trainer for the relevant expansion. (WoD you just mine or herb the first one ypu come across and the game gives you a scroll for learning WoD gathering).
-Bugs- There aren't too many glaring bugs anymore, but you will certainly encounter some. The pathetic thing is that many of the bugs you'll encounter were reported repeatedly during Alpha/Beta and still weren't fixed. Some bugs were discovered after release and players were able to abuse game mechanics without repercussion unless they were one of the more serious offenders. This gave some players a significant advantage over others because they used exploits and at the start of an expansion, that is the time when it's most impactful.
Special mention is the Darkmoon Faire Top Hat and WHEE! buff. While not always available due to the DMF being inaccessible most of the month, if you happen to be leveling when the DMF is running, it might be worth your time to go and get these. AFAIK they do stack with heirlooms, although I have not personally tested it. Fair warning: These buffs do NOT stack with each other, and the hats disappear after the DMF goes away later in the month(unless you only log in when the faire is running).
We’re also big fans of Simple Armory, which gives you a similar look at your overall progression acrosss the entire game, as well as a gorgeous, detailed graphical listing of all the achievements you’ve unlocked and all the mounts, companions, pets, and toys you’ve collected. The site makes it incredibly easy to see what you still have to get, if you’re a completionist. If you’re looking to fill out your collection of mounts, the site will even create a handy, optimized guide of how you should spend your day (or week) adventuring to acquire them all.
Zygor Guides is an in-game software strategy guide for World of Warcraft. Every guide comes complete with the Guide Viewer, which displays step by step instructions of what quests to accept, how to complete objectives, when to use items, and more. Our gorgeous waypoint arrow will point you exactly where to go at all times and the model viewer will display fully rendered 3D models of NPCs and objects mentioned in the guide.
Professions: This may seem strange for a leveling guide, but the first opportunity you get, pick up both the Mining and Herbalism gathering professions. Not only will this allow you to track many various quest objectives on your map, but you also get a fair amount of experience whenever you gather. I'd put it at around 10% of a quest turn-in per gather. Since most of your wasted time in WoW is travel time, stopping to gather ore or herbs can keep your exp/h rolling as long as you don't go too far out of your way. You should only gather if it's convenient, and on the way to an actual quest objective. Don't make gathering your priority.
Dugi’s leveling guide is the leveling addon I’ve always used to level as fast as possible. It will show you where to go and what to do in-game, speeding up the leveling process. This is optional though, as the game already does a pretty good job at showing you where to go at all times. The addon does, however, come with a couple of other nice features and perks.