Pretty straightforward question. There are a lot of things I like about Ryzom, but if I had to pick one thing, it would be how "alive" the world feels. Animal characteristics, sounds and behavior, weather effects, scenery and other smaller details all make for a rich world. It has the best world I've come across in any MMO I've tried.

adaptability:

from interface colors, positions, window sizes over building your own actions, options upon character creation (though we could do with some new haircuts *wink*) all the way down to the Ring where you can build your own scenarios (though the ring is, as we all know, far from perfect).

Power to the players ;)

Community, its all about the people :)

There's a lot more, but that's the answer i will always give to a favourite thing in an MMO question.

Now if you'd asked what makes Ryzom unique....

I prefer the way you can modify crafted items by changing the materials used.

The whole ecosystems behavior that makes me think to be in a virtual world and not in a game.

The one thing that I would have to name is the way the animals act.

You can see them attack another one, they are not just standing there.   The migrate around and just makes you feel a real world. 

Mob AI

The whole "feeling" of the game. Including:

The not "black & white" storyline. The whole lore is (almost) unique.

The graphics. Yes I´m a fan of the franco/belgique comic style.

The nice people around ;)

The way players can contribute to the story by their actions in the life events.

I just love it

CU

SaM