Hmm, my answer doesn't appear so I guess I won't vote.  What made me want to work at the mud I am at was a combination of things:

Although we are still small, the players and immortals all really care about each other.
The mud is mostly original and fun to explore as a player.
The coder is always adding new things.
The mud is very stable...  most of the time.  (see new things, above)
RP is fun and encouraged but not required outside of the PK system.
Most of all, I guess, I wanted to be there as an immortal because several of the existing immortals wanted me there.

'Nuff said.

People who don't double post. 'Nuff said.

-D

Game integrity is the most important aspect of a game to me.

Where the staff works together to present their vision and doesn't sway from it to placate anyone. Where improvements benefit the game, rather than an individual player or individual staff member. Where mechanics AND gameplay are consistent with the genre, the overall theme, and the intent of the game.

Where the game attracts players who share in the vision, and *highly* discourages disruption, through enforceable policies.

Where policies are enforceable and enforced, whatever those policies may be.

This applies to any type of game, from Monopoly to Chess to Godwars to custom muds to King's Quest to baseball.