Can you own a house is it instanced? Or is it out where everyone can see it?
Can you have pets? Do they have to eat to live? If they die are they perma-dead, or can you rez them? Can you ride these pets?
Is there item durability? If there is, can items be repaired as many times as you wish?
Can your avatar learn skills from other classes? If so, can you learn all of the other classes skills, or is it limited?
Is the movement click-to-move. Or is it WASD based? Looks like it is click to move - cool!
Is there an off-line messaging system (e.g. a post office to send messages and items to offline players)?
Is there a bank or warehouse? Is it shared among all of your avatars on a server?
Does your avatar need to eat to live (other that healing potions in battle)?
Is there an Auction House, or some other method for selling items to other players when you are offline? How many days can you leave items in the auction house?
Is it possible to gimp your character? For example, in Maplestory, you can easily mess up your HP build if you don't put points in certain skills at certain levels. Is Mythos like this at all? (I hope not).