Must have WoW addons
World of Warcraft's hotbars are easily the most outdated part of its user interface. By default, they're quite small, can lack crucial information, and you don't have a whole lot of customization options. Enter Bartender, an addon that gives you full control of ten action bars including their position, size, and even transparency.
If you're starting out in World of Warcraft as a brand new player, this should be one of the first mods you consider. Before long, your hotbars are going to fill up and become an annoying mess. Bartender lets you set keybindings and position them perfectly for an optimal setup. More advanced users will appreciate the ability to program custom macros that can change the state of your action bars too.
The other major addon that you shouldn't be without, Deadly Boss Mods makes World of Warcraft's complex boss fights a little more approachable by providing real-time alerts to keep you one step ahead. With this addon (and its other versions for older expansions) installed, you won't have to painstakingly memorize every boss fight. Alerts and camera effects will warn you of dangerous attacks or give you simple instructions. Raid and dungeon timers are synchronized between other members of your group, which keeps everyone on the same page even if one player accidentally disconnects.
What I really love, however, is a tiny feature that auto replies to in-game messages while you're in a boss fight. This optional autoresponse will let whoever whispered you know you're kinda busy and tell them how much health the boss has left so they know if things are going poorly.
World of Warcraft's inventory system is kind of a mess in the default version. Instead of having one large inventory, you have separate bags that store all the stuff you find while exploring. It's cumbersome to deal with, but Bagnon makes this nightmare go away. It replaces the entire inventory window with one large bag that stores all your items, but its other features are what makes it a must-have.
For one, you can view the items (even if they're in the bank) of all your alternate characters on your account. Icons also have special coloring based on item quality, helping you more easily discern rare items from trash. A search engine in the inventory window makes finding specific items even easier and there's the always helpful sort items option, which cleans up your bags and groups relevant item types together.
You get one guess what this addon does. MoveAnything is a powerful tool that lets you adjust every UI element, giving you complete control over not just your action bars but quest list, portrait location, minimap location, and more. If you've ever wanted to fully redesign WoW's UI, this is a good place to start.
Total conversion and immersion addons
This is one of the most popular total conversion addons for World of Warcraft. ElvUI replaces every single user interface element with a sleek redesign that is a lot more modern and readable. The tradeoff, of course, is that you're also getting rid of the fantasy themed UI altogether. You also have to install and update it manually, but it's not too much of a chore. What ElvUI brings to the table makes the sacrifice more than worth it because, along with the overhaul, ElvUI offers a ton of customization and also includes a suite of addons like TidyPlates that help clean up the look of WoW's aging interface.
One of my favorite parts about ElvUI is that it comes with an in-game setup process that'll help tailor the UI to suit your needs. There's class-specific setups that emphasis the interface elements most important to your role, and the settings have a ton of options to play with. I particularly love how the action bars behave in ElvUI, and its built-in addons means you won't have to fuss with other addons like OmniCC. Just beware, if you want to use ElvUI, install it first before bringing more addons into the fold because it doesn't always play nice.
In patch 7.3.5, World of Warcraft introduced dynamic level scaling to all of Azeroth, entirely changing the way you level new characters. It's a great time to start a fresh character and experience Azeroth from a new perspective—literally. Using the Action Cam feature that was implemented in an earlier patch, Dynamic Cam shifts the perspective to make WoW feel more like a third-person action game. By doing so, Azeroth has a sense of scale that makes it feel wondrous and exciting again. What's great is that Dynamic Cam automatically shifts between different camera positions depending on what you're doing, which Action Cam can't do on its own.
If you're leveling a new character, this is a fantastic addon that'll make your time in Azeroth feel more immersive and intimate. You just can't appreciate the size Ironforge using the usual, zoomed out camera.
Combat addons
This addon is tiny but oh so effective. Basically, it adds text to your action bar icons so you can better read how long the cooldown is on your abilities. There's some nifty customization options, like being able to determine when the cooldown timer starts showing fractions of a second (if you want to be really precise with your abilities). But OmniCC is the kind of addon that does one tiny thing, and does it very well.
Details! Damage Meter is a very accurate graphical DPS meter that shows how much damage you and everyone in your party is doing by sifting through the combat log. If you're playing a damage-dealing specialization, I cannot stress how important it is to have Details. Not only will it help you up your game, its optional tools are a godsend, like being able to see the talent choices and item level of your party members.
You might think that only the tank would need a readout of monster aggro, but you'd be wrong. Omen Threat Meter also helps healers and DPS by showing each party member's relative aggro for whatever monster you are targeting. That way, you know if you're in danger of stealing aggro from the tank or, god forbid, if the tank dies who the monster is going to target next. In high-level raids and dungeons, having that kind of information is invaluable
Easily the most complex addon on this list, Weak Auras 2 is a framework that lets you display special graphical elements on screen to indicate buffs, debuffs, and other relevant status effects instead of just bombarding your eyes with more numbers and meters. There's an insane level of customization available here, from using custom sounds (like Owen Wilson saying "Wow!") to class-appropriate visual cues. It can be a lot to take in, but meralonne's video guide will get you started. The great thing about Weak Auras 2 is that, if you don't have the energy to program your own custom ones, you can easily import templates from other players. Here's a website with a massive list of pre-built Weak Auras 2 scripts you can use.
Quest, profession, and miscellaneous addons
World Quests are a new type of temporary daily quest first introduced in Legion. It's a great system that suffers from World of Warcraft's outdated map interface, but World Quest Tracker fixes those problems. From a zoomed out view, World Quest Tracker shows you the rewards available from World Quests in each zone, so you can quickly see if there are rewards that are relevant to your goals. From there, you can simply click on the reward icon to automatically track multiple world quests in your quest window so you don't waste time having to check the map again and again. World Quest Tracker also has a stats screen that tracks how many world quests you complete, cumulative rewards, and more.
Once you've finished leveling your first character to 120 in Battle for Azeroth, you probably aren't keen on doing that whole process over again with another character. Enter Azeroth Auto Pilot, a speed-leveling addon that automates dozens of tiny things to make grinding a new character to max level even easier. With this installed, you'll have an arrow that guides you from quest to quest in highly optimized path while the addon handles all the little things like talking to NPCs, interacting with items, and more. Really, it's like leveling a new character on auto pilot.
There's been a lot of controversy in the community over Blizzard trying to limit addons that automatically place you in groups for World Quests, largely negating the need to even participate in the quest to complete it. LookingForGroup is a nice compromise, though, that makes it easy to instantly find groups without having to comb through the cumbersome group finder interface. Once you reach level 120 in Battle for Azeroth, it's a great tool to help make knocking out those daily World Quests a little easier.
For you crafters and gatherers out there, Gatherer is a must. The addon shows the location of mining, herbalism, and treasure locations on your minimap. It does this by remembering the location of resource nodes that you've previously found. That doesn't sound all that handy because you'll need to find those nodes to begin with, so import the GathererDB from WoWHead. This contains data for all the possible node locations in Azeroth, and Gatherer will always point you toward the location of precious resources.
If you fancy making a bit of gold in World of Warcraft, Auctioneer is going to become your best friend. This complete overhaul of the auction house interface can scan the market to track bids, buyout prices, and quantity of items sold. Simply put, it gives you all the information you need to make informed purchasing and selling decisions on the auction house. One thing I love is that item tooltips will now display a recommended selling price based on some black magic and statistical math. Another amazing addon included in this suite is Bean Counter, which tracks your bids and postings to give you reports on item-specific profitability, helping you identify what's really making you money.
That's just the tip of the iceberg too. Enchantrix shows you the value of materials from disenchanting, milling, and prospecting. Informant tells you if the item is relevant to quests or a certain class. SearchUI will notify you if there are auctions that fit your criteria for buying or bidding. The list goes on and on.
This one is real simple, OPie creates contextual radial menus so you can easily use certain abilities on your action bar with just your mouse. It's not a necessary addon by any means, but it's sleek and simple to use. I love freeing up action bar space and dumping seldom, but still necessary, actions (like Demon Hunters' spectral sight) on the radial menu.