The basic idea was sound, however, the implementation was not all it could have been. The Uncle Pumpkinhead MOBs should have been somewhat more plentiful and found in every non-city zone at apropriate levels for that zone. They should always have dropped something of interest loot-wise, which does not mean they should all have dropped some unique or special item.
Maybe the 'special' loot should have been some sort of themed one-shot item such as 'A Pumpkin Lantern' which could cast a special fear nano on use capable of scaring off any one MOB (that didn't otherwise have immunity). That may seem powerful but being one-shot they'd not hang around foever, so their one-use naure would have balanced the power. I'm sure other suitable ideas could have been thought of.
The special loot items that did sometimes drop were an interesting idea combined with the low spawn rates did rather lead to camping and kill-stealing which I think we can all agree are bad. There isn't any easy answer to that if you want to put rarer items into an event like this, but perhaps having two different types of MOB, one which drops more normal loot and is quite common, and another which always drops something unusual but is rarer. That way people who just want to have fun can go and hunt any of the MOBs but people looking for the unusual loot will only be interested in the second type and be likely to leave the more common MOB type alone as it would have nothing of any interest to them.
This is where something like the so-called dynacamps could work well, if they were actually dynamic. Every playfield would have 25-50 invisible placeholders and every playfield would have a spawn rate and maximum cpacity for the dynacamps. Every time a new spawn was due, if there were already the maximum number of bosses, nothing would happen, but if bosses had ben killed, a new camp would spawn at one of the placeholders picked at random that did not already have a boss. The boss would be of a type and level suitable to that placehlder (a placeholder would have several types that could spawn, and a range of levels they could spawn in). Once a boss was killed, the camp itself would be despawned after a short delay and any remaining minions not in combat would also despawn.
More events like this are welcome, but desgning them well (and where necessary changing the game) should be considered a priority for a future patch. Adding greater flexibility in dynamic content should be considered essential to the game's future, and would allow more interactivity between the player's and the 'story' with less effort on Funcom's part than currently seems to be the case.
And, to steal an idea from some other bloke, come xmas, bring back the pumpkin heads..