There's something to be said for giving players a fixed set of armor and equipment upgrades to strive for, that perfect set of stat-enhancing items that let other players know exactly how accomplished they are. That something is "boring."
Any dedicated World of Warcraft player can look at another and suss out exactly what pieces of equipment they are wearing, what bonuses they are getting to their attributes, and generally how hard it would be to take them down, should the need arise. The intimidation factor is gone.
Now mix-and-match separates? That's scary.
Look at this woman.
I have absolutely no idea what to expect from this woman. I do not know what weapons or tactics she uses. I cannot see what talismans and trinkets she's wearing, so there's no way of knowing how powerful she is. She's just a professional woman standing in the middle of an ancient, monster-filled temple.
She's scary as hell.
Funcom has been giving player social outfits to tool around with since Anarchy Online, giving role-players a wide variety of outfits to mix-and-match. The Secret World does away with stat-based armor altogether, giving players in-game clothing stores, clothes as achievement rewards and special items in the free-to-play game's cash shop.
Free from stat-enhancing shells, players are free to express themselves through clothing. Sure, some still opt to wear armor...
... but many more choose to look like this:
Funcom has posted a guide to The Secret World fashion over at the supernatural MMO's website, explaining how players can look unique and original like the people in these screenshots. Hopefully they can also post a guide showing other online games how to take off their armor and relax.