World of Warcraft players, come in!

I don't understand how the default interface is "clean" when the chat and raid frames take up half your screen, you can't tell how much health and mana you have without glancing at the corner of your screen, and two edges of your screen are filled with buttons; just saying. Rusty puts his frames in the center of the screen and changed the size of his chat box, so if that works for him, I'm not gonna tell him it's bad.

 Addons I use, most essential in bold

Bartender4 - my most useful addon. Lets you customize your action bars. Make your bars the length you want them to be, in the spot you want them to be, the way you want them to look. Makes changing your keybinds super easy too. Before Blizzard let you move the unit frames around, I could not play with the default interface.
Deadly Boss Mods - pretty much a requirement for raiding. Even people who swear by the default interface use this.
Omen - threat meter. Useful if tanking a raid.
OmniCC - prints CDs in number form in addition to the radar sweep for more accuracy.
Pitbull4 - just not a fan of how the default unit frames do not show life/mana in number form, and how tiny the bars are compared to the overall size of the frame.
PowerAuras - custom alerts for anything, super useful for DPS.
Quartz - cast bars and debuff timers, you seriously need this information in some form if you want to do half-decent DPS.
Recount - combat log parser.
SunnArt - just makes the interface prettier.
TidyPlates - makes health bars prettier and tracks debuffs on multiple targets. Really good if you're playing a class that multi-dots.
Vuhdo - raid frames that make healing 10x easier.