In this particular case I've tried a game called Evony. It is a role playing game, you have to create a character and, with other players from all around the world, you have to complete some tasks.
Not talking about the fact that playing this game is interesting and motivating, it's a good game to practice conversation and vocabulary. In this game you can communicate with other characters by chatting, and students can learn a lot from other players. Also the game includes a lot of vocabulary, and also instructions which are obviously in English, so we can say that is a good way of learning.