Kill monsters, level up, kill monsters, level up...
You start off on an island that acts as a tutorial. It teaches you all the commands and many aspects to the game before sending you off the the main island. On the main island (if you are level 8 or 10 (depending on which "job" you desire)) you go out and become one of the 5 jobs available. The 5 jobs are: Warrior, Magician, Archer, Thief, and Pirate. All very unique, all much different in attack style and power. Each class has "skills" some used for attacking monsters, and others used for personal gains such as extra attack power.
Each time you level up, you receive 5 "Ability Points (AP)" which are used to increase your Strength, Dexterity, Intelligence, and Luck. Each time one of these abilities are increased (depending on your class) your power is increased. You also receive 3 "Skill Points (SP)" which is what I was talking about in the previous paragraph. You apply these 3 SP to a skill of your choice. However, these skills take many "level up's" to max. Some of the skills max at level 30, which is 10 level ups. Leveling up, can, and will, take a very long time in later levels. You will be attacking monsters for several hours before you level up. This can get very, very boring.
Dying in this game is unique to any other game. When you die in Maplestory, a gravestone drops down from above you, and you become a ghost. When you are a ghost you cannot do anything except for "think" (talk). A message will pop up saying "blah blah you have died, you will be returned to the nearest town". When you click "ok" you are spawned in the nearest town to your death and you will have lost experience points. Some jobs such as Warrior and Archer lose twice as much experience points as other jobs such as Magician and Thief. The amount of experience points you lose is determined by your "Luck" which Warriors and Archers do not increase.
Unfortunately, all great games have to have at least one flaw, and for Maplestory it is a major flaw. It is called... "The Cash Shop". "What is the cash shop?" you say? The cash shop is a place where you can change almost anything about your character. Anything from changing their hairstyle, changing their clothes, changing their name, and many, many more. Sure this sounds great, but of course, these great items and benefits can only be purchased with real-life money. These items are not necessarily cheap either. Simply buying some clothes for your character may cost up to 20-30 dollars, depending on which clothes you buy. And a simple name change? 10 dollars. Sure it may not seem like much to some, but when you are going for a full makeover of your account you are talking some serious money there.
If you are going to play Maplestory, please, please do not get addicted to buying items in the Cash Shop. Many Cash Shop users have compared the cash shop to drugs. Saying they are that addicted. I myself was addicted to the cash shop. My clothes, or my hair was never good enough, or got old, so I had to change it. I used nearly 125 dollars in 3 months! That is ridiculous. If you are going to spend money on the cash shop, please set a limit for yourself, because Nexon (In charge of Maplestory) ain't gonna do it, they feed off of the cash shop purchases, that is where their money comes from, they don't care how much you spend, as long as they get their money.
Overall, Maplestory is a good game. If you are looking for more than just fighting monsters and leveling up over and over again, then maybe this game is not for you. But you never know, go ahead and try it, it may just be "your game".