As a player who recently started playing MapleStory again, I would like to see the return of the Lab Server event.

The rewards from the Lab Server I feel are critical to progression are the legion block rewards:

Legion Block Details:

The level of the Legion Block is based off the maximum level your character reaches in Lab Server.
At Lv. 60: Grants Weapon ATT/Magic ATT +5
At Lv. 100: Grants Weapon ATT/Magic ATT +10
At Lv. 140: Grants Weapon ATT/Magic ATT +15
At Lv. 150: Grants Weapon ATT/Magic ATT +20
At Lv. 250: Grants Weapon ATT/Magic ATT +25

Enhanced Legion Block Details:

The level of the Enhanced Legion Block is based off the maximum level your character reaches in Lab Server.
At Lv. 60: Grants Weapon ATT/Magic ATT +7
At Lv. 100: Grants Weapon ATT/Magic ATT +14
At Lv. 140: Grants Weapon ATT/Magic ATT +21
At Lv. 150: Grants Weapon ATT/Magic ATT +28
At Lv. 250: Grants Weapon ATT/Magic ATT +35

(Source: http://maplestory.nexon.net/news/34318/lab-server-here-for-a-limited-time)

The two Legion blocks obtained from this event can offer up to 60 Weapon ATT/Magic ATT and these blocks also ignore the member limit on your legion. This can also allow you to have additional boosts as the blocks occupy 9 additional grid slots on your legion.

I feel that this significant boost in Weapon ATT/Magic ATT creates a progression gap between the players that completed the events vs. those that did not have a chance to participate.

I would like to see a return of this event in the future. This would give existing players and new players a chance to obtain these great rewards.