That's not bad actually. The mayhem ensuing when you throw that many people on something is always insanely fun and doesn't get old easily^^ It's also spot on on the MMO mentality. LOTS of people together.
Druckbare Version
woot, i updated my suggestion after i saw you revived this thread ^^
A mix between the two could work as noted, you need instance for balance, just look at the "invasion events" we have. The main baddy gets pwned in 10 seconds cause 50+ are just ripping him to shreds lol. Kinda like, there could be baddies outside/in tower you have to fend off in order to unlock certain instances but if you don't keep the horde at bay then you may lose access to certain instances til you succeed in fending them off in the open world.
Castle Zvahl {Can I have it!}
How about a open world dungeon with closed doors? You need to get a key from a specific mini boss to unlock the door (but only for you and your party). And the further you progresses in the dungeon the lesser the crowd get, because they need to win the claim war for the next door first ^^
And the end boss is behind the last door and it can't be unlock while there is already a party behind.
Crystal tower in concept just screams Nyzul isle, I can't see it not being instanced.
Some stuff is fine instanced and this sounds like a concept better placed in a instance than open-world. Wouldn't mind it having some elements outside of the instance though like quests that are unlocked the higher up you climb.
Oh, I really hope it houses a boss gauntlet ala FFIII. Member dies on the second boss of four? They're gone for the remainder of the sequence~ Would make for some awesome 'skin of your teeth' style encounters!
Sorry, what you said seems to be contradicting. If it was not instanced, there would be more players and so the content would be easier?
Stronghold is open world but its not very interesting if you take a bunch of players in and zerg (the point of open world?).
I hope crystal tower would be something like the LABYRINTH OF TIME from FF1 remake, where you put restrictions/debuffs on your party to increase reward (or the time before the better exit portal closes in the case of FF1). Then a boss at the end depending on how hard you made it on yourself with the restrictions/debuffs.