This was personally a lot of fun for me, as it was probably for all of us. I wish there were more people online to join in, but things like this will keep server activity going-- I'd definitely go out of my way to show up to these. Thanks for setting all of this up for us!
I personally enjoy the zombies the most, and love the idea of zombie apocalypses. I think this gave some ideas for a future PvE arena, and I hope that we will see more inspiration to build PvE arenas in 1.9. Do keep in mind that PvE arena do act as semi-automated experience and item farms in light of
recent discussions in the economy topic for 1.9, more or less easy depending how easy it is to kill mobs. I would be interested in using my plans to build a Mega Mob Masher (my personal design for a mob farm) to not only be used as a mob farm, but to hook up a long-planned component of it to make into a PvE arena. The Mega Mob Masher (MMM) is currently capable of producing 80 mobs/minute, in the variety of zombies, skeletons, creepers, spiders, and witches, and is precisely the rate mobs would pour out at in the PvE arena, if made. I could even design a mob-sorting system on the MMM, so that you can control which type of mobs you fight, and which ones get left out and burned.
In general, I would like to see more activities for PvE (and PvP) in the mix with any of the treasure hunts that we've been discussing. I'm actually building a PvP arena right now in the swamp on the current map that should be ready for release and usage soon-- you can see it on dynmap
here. Perhaps we would be able to get this worldguarded so players don't have to worry about accidentally breaking things or causing mobs to grief it?