One thing I would like to add if Hamlet defense works in the same manner as Besieged/Campaign:

DON'T limit participants like Behest currently does! Campaign has no limit (multiple zones), and Besieged I think had a very high cap (100 players? Tell me if this isn't the case.) for those that could jump into the battle zone. To get a large portion of the server in on things are very fun.

And make sure the mobs don't die in 5 seconds.