Maple Story's younger and "special" brother.
I will start off telling you the classes. What's that? You already know the typical generic classes of mmorpg's and Maple Story. Ok, then we will skip that. I do feel I should tell you the Skill system is more difficult in Wonderking than Maple. The stats are the same only vitality and wisdom probably have a use in Wonderking unlike it's older brother; wherein, only hp-washing is useful.
Graphics... What you already know what maple story looks like? Wonderking's graphics are slightly better and smoother than Maple's, as we would expect from it's being released in 2009/'10.
The quests in Wonderking are much better as they give great experience, unlike Maple story. The thing is, just like in Maple, there's so damn many of them. You will be grinding a lot as well. Grinding can be hindered is you mess up your skill build - same with PvP.
.
So why even play? Some people might say for the PVP! I have seen the classes and their skills and I know not all is balanced. I will also say there is a big problem with lag and map generations between individual computers. PVP is not even out as of now. I have now played the PvP (2010) and while it is not balanced, it adds fun to the game and a certain depth.
It is a lot easier to level in Wonderking than Maple; however, it still takes a bit of time. The level cap in WK is lower as well.
My favorite feature was the talking NPC's. They were cute and animated voices that made the experience much better.
The biggest disappointment in WK were the bosses. The bosses are very lame. It is nothing like Maple's bosses (not a good thing imo). The bosses are more like a Megaman style and they move quite quickly and lower HP and lvl classes have an extremely hard time surviving.
There wasn't a lot of team work going on in WK. And just like in Maple there is a lot (probably more in WK) of KS'ing!! Many of your fellow players do not speak and just ks.
There are features like mining and crafting, nothing really special about them. There is also a micro-transaction system to support this free to play game.
Overall: I say Wonderking will rival Maple Story in the future (as of 2011, it seems I was wrong as Maple's population only seems to increase probably due to Nexon's advertising). There will be two types of players fighting about them. The players who like to join parties and fight epic bosses and the players who like to PVP (but soon Maple will have PvP so now I am thinking Wonderking will stay at a moderate population and eventually taper off).