First off Graaloween isnt Graaloween without Club Crypt.
As for the main event: I absolutely loved trick-or-treating the past two years. However, now that the playercount is almost constantly above 3000, I feel that the system could be a little less competitive (ie private spawns; similar to loot spawns; only you see a particular spawn).
Or is this system being completely done away with? (I hope not :cri). If the system is going to be completely redone:
Then I'd like to see "traditional" trick-or-treating, where you are receiving the candy (whereas in previous years, NPCs were the trickortreaters and you gave them candy; "reverse" trick-or-treat). The candy can be converted into a random prize (hat item gralats etc). You can even get creative to make it a little more difficult than just walking up to NPCs around the map. Such as, the player must dress up an exact way to receive their candy from that NPC (either dress up exactly as the NPC, or have a "model" image appear. free default heads, bodies, and hats can be used).
Or find another twist to put on trick-or-treating. But I honestly dont see much other than trick-or-treating that can be repeated. A miniquest (such as halloween 2011) is out of question, because no one will want to do it 2 years in a row. The witch hunt (2012 i think) was unique, but again, not repeatable.
Oh yeah! just now remembered this one: The Zombie Apocalypse idea that was thrown around the last few years. I still think thats a really good idea. Zombie baddies infesting the entire map; not even Graal City is safe. Prizes rewarded on a basis of how many you kill, or have drops.