I played on the global server before moving to a high rate server. Both, I've quit.
At first, the game is somewhat addicting.
However, as you level up, you notice there isn't much to do besides level grinding, Devils Den, Castle, or Golden Event which involves usually just mass killing again.
There's hardly any quests, or much story behind the game either. A lot of level grinding, lack of quests.
I played Ragnarok Online for about 2 years, so I recommend giving that a try if you haven't already.