I like the degree of coordination that the mission takes; rather than just going down and doing whatever, you really have to talk to your team and clear out the floor in a methodical, even agile, way that really makes the game's potential shine out.

The only issue is that this is an event, and that it becomes predictable. Its very very easy to define the event like so:

if Harvester is chasing you:
----Distract the Harvester as long as possible
else
----Farm the gravestones and solve puzzles

What the event needs is for some kind of variation on the Harvester's attacks, as well as the tombstones, as well as the format on the whole. For instance:

Gravestones spawn: (Choose 2)
-Bombies
-Scarabs
-Various Gremlins (Apocrean Themed)
-Silkwings
-Shadowy Glop Drops
-Swarm elements and monsters
-devilites

Additional Elements: (Choose 1 or rarely 2, if any)
-Pentagram that summons deadnauts at the start of the level
-Battlepods
-2 Tortodrones
-Maulos
-Giant Green Jelly
-Black Kat

Harvester Attacks: (Choose 2)
-Area effect of grabbing hands
-Soul Sucking
-Spawn reskinned howlitzer heads in circle around boss
-Move while soul sucking; deals status effects
-Area effect of grabbing hands that effects larger portion of the level

Level variants: (Choose 1, if at all)
-Large hole in middle
-Divided by walls with gates and keys
-One way gates

Something like this would increase replay-ability by a large margin, and is really what I expect from a game about random generation in MMOs.

That said, its still my favorite event and I think they did a great job on it. Last Halloween. :l