After a quick look:
New Medic Gen: Sure will have his uses but probably only as a sac gen. sent 200k at a camp came back with i think 69k... first aid skill added didnt seem to make much difference. Maybe adding a built in 1up would improve his worth abit more?
Settlers Headquaters: not really sure on use of this.. acts as a store but without storage and only 20 pop... for the size of building i would have expected a higher pop.
New buff building: Buffs look handy from what i could see. However, the building is massive! and like other new stuff is not levelable only multiple reduce cooldown. More needs to be known how the buff works with regards to xp bonus.
New islands: Space is always welcome although half the island is at the moment unusable I am guessing that will be for future deposits or something else in future. Having it only available through gems though is very disappointing! Would really like to see an option of a resource available in game such as stalks. Not all of us can throw money at the game.
New nuke (crossbow or something): works like assassin but only for a single leader.. could be very handy on some of mountain clan campaign camps i imagine, but currently cant be used along with a normal assassin which is a shame.
Balloons: Only seem to be able to make in festival building for resources, shame you cant get from adventure as well as I think this would add to the event if the drops were decent. I understand main total will be based probably on player count overall... please BB make sure you dont count inactive accounts as on Zeus sever are probably more inactive than active accounts.
Candles and dough: From treasure search and collect on home island only i think? maybe drop on adv also but didnt try. Hopefully drops are enough as it looks like you need 300 of each daily to get the 100% buff for hall.
Overall looks like a very communal event, which as long as everyone works together and not try to individually profit should be great!
Hoping the placeholders get replaced with some other awesome stuff!! Maybe level specific? Like stronghold for over 70's?!
(can but dream).