I have played lots of MMORPG's but this is certainly the best
And there are two types of level,the base level,that when you level up you gain maximum HP and SP,and points that you can spend in attributes that are:Strenght(STR),agility(AGI),intelligence(INT),vitality(VIT),dexterity(DEX) and luck(LUK).Str makes you give more damage with physical attacks,and increases the amount of weight that you can carry.Agi increases your attack speed and your flee.Int increases your maximum SP and your magical attack.Vit increases your defense and HP.Luk increases your critical chance.Dex increases your attack with bows.
And it also has the job level,that when you level up you earn a point to spend in your skills.
All persons starts with a novice.When you level up till level 10 of job,you can become class 1 that are:Swordsman,Thief,Archer,acolyte,merchant and mage.Or you can become one of the expanded classes that are:Taekwon,Gunslinger, and Ninja.
At level 40 of job you can evolve into another class.Swordsman can become Knights or Crusader.Thiefs can become assassins or rogues,Archers can become hunters or bard,if it's a man,or dancer,if it's a girl. Acolytes evolve into monks or priests,Merchant blacksmith or alchemists, mage wizards or sages.The expanded classes have no evolutions.They can reborn after that and become even more powerfull,and then become third classes, that can level up till 150 base level and 50 job level.
You can spend your attribute points in many ways for each class.You can use lots of builds that gives you the possibility of having different playing experience using the same class.
Overall,it's a very good game.You may get sick of it and stop playing for some time,but you will get back.