Suggestions and ideas

Class balance:
Warrior is, perhaps, the weakest class in the game. It is missing 2 skills at level 25 while archer has all skills at the same level. At level 25, I can rarely see a warrior.
Warrior is weak because of melee attack and less useful skills when comparing with other classes.
For example, archer has 2 skills that can root enemies and 2 skills that can knock-back enemies. When fighting against melee class, archers usually win without being hit.
Warrior's skills:
Restore: It is quite useless because we can use pots and save skill points.
Iron Blood: only 20 extra armor at level 5, and it lasts too short.
Knock-back skills are almost useless when dueling with ranged units.

In game functions:
Trading system, between in-game-mates
A place where we can forge items
Auction house
Quests
Messaging between friends
Ranking system
Bank system, also allowing us to transfer items between character
Looting system: Roll for needs

Better use of low level dungeons and increase sale:
Instead of getting equipments from those low-level dungeons, we will get materials from them. Each material will be used to forge our own equipment.
Such new function will not only maximize the use of those dungeons, but also increase the sales of dungeons.

Keep coming...