Grand Chase 

Grand Chase is an online fighting game originally developed by KOG Studios. The game is commonly confused with a MMORPG or an online Adventure game. Although there are many elements of those types of games in here, it is not an RPG. The focus is on fighting, like in such games as Street Fighter, but online. Yes, it does have a storyline, quests, character creation and so on, but it is mainly focused on button bashing, the arcade mode of fighting games.

In Grand Chase, you do create and customize your character, then set out in a 2D world in conflict. You gain experience by completing quests, which are really well done. In fact, the 2D environment doesn't do any damage to the game. The scenarios are well designed, and the graphics look good enough. The combos and fighting moves you can make are really greain, just as in a solid arcade game. There is also a lot of PvP combat, if you can find some players on the servers you are playing. After a while, without PvP, the game becomes a bit repetitive though. Grand Chase is really an interesting concept for online games, and it can be very enjoyable. Give it a try, it is free after all.