Something unique about kal online is the assassin mode which is in effect when u put on an assassin mask, changing your name into ASSASSIN in red color which will completely hide your character's identity to others and allow you to attack other people (your identity will remain hidden even when u kill other people. It only reveals when you are killed or when the time limit of the mask is over which is over 30 minutes I think). It also takes away your ability to teleport, making it more thrilling. A party of assassins in kal online is something to behold cause it creates chaos and fear among other players and is also very exciting for yourself knowing that if you're killed, you may drop items.
example video of an assassin party:
http://www.youtube.com/watch?v=CNgpC4iZzBsThe other unique feature of this game is the every weekends castle war, a very huge battle between 2 sides, attackers vs defenders. Each side exist of the alliance between many guilds. The alliance that holds the castle has many advantages during that weak, like receiving a percentage of all that is sold by the NPC's to players as a tax (they can also change the prices and so), and other stuff I cant remember atm.
example video of a castle war:
http://www.youtube.com/watch?v=LKEiJpNFh2sThere are also unique mobs in game which require a great amount of players to defeat.
The economy in Kal online is very interesting also, its like a game on its own.
Another unique feature of kal online is that all characters have an egg they receive early in the game which then develops with them as they progress in game and at a certain level it changes into the animal they chose for at the beginning. It gives extra stats and you can transform to this animal for abilities suited for your class.
And if you are nerdy enough, you can leave your character fishing whenever you go sleep or go out. lots of medicines and "soups" are made from fishes people catch, for example speed up medicine or...