In general this is a good event. Here are a couple of ideas for future iterations.

I would suggest in the future that they add mana pots as a drop - burn through a ton of mana pots fighting a boss, and what is the fun of castle siege if you aren't fighting them.

In future versions it would be great if there were some way to change factions - kinda sucky that I can't fight in 1/3 of the castles.

Also would be cool if they were able to add a castle siege only open chat. Guild chat is available, but I am the only person from my guild that participated in castle siege and so it would be nice to be able to communicate with other players.

Another idea would be to allow for a player to actively engage in a counter attack to defend the their factions castle. Doesn't make sense that I can walk up to the castle where my player is garrisoned, see that it is under attack, and do absolutely nothing about it. It would be great to have an option like "join the defense" which if selected would engage you in the defensive forces, instigate PVP battles which either reinforce the defense or weaken it depending on the visitor of the fight, or allows engagement in some other fashion. Right now it just seems to passive.

We also need a better understanding the benefits of, or incentive to, hold castles, garrison yourself in a castle, etc. still lots of explained stuff that is not apparent even after multiple hours/days playing siege.

Very important to create a much better reward for defeating a boss. I mean these guys are over 40 million hp and 150k or so attack. That is a formidable opponent, especially solo. Should be rewarded with a random 5* card with a remote - 1-2% maybe chance for a boss drop or legendary.

There is currently no incentive to complete a boss fight. Castle Siege on my realm is literally littered with fights that have been initiated, but never completed. I mean there are instances where with a few minutes remaining the wall and gates are still not attacked. I think that there should be penalties - loss of PVP points, penalty box time that prevents you from participating in a boss fight for x amount of time, etc. especially if you are the one who initiated the siege, but did not finish it.

Just a few thoughts for Kabam and other players to consider.