1. Identify a boss design that seemed good for its time. In what ways did it favorably shape its combat experience. How might that be taken further or additionally improved upon (by whatever other means)?
Theres actually quite a few bosses, dungeon or not, that i think have some very interesting concepts that arent seen much anywhere else.
For instance, the first boss of the Great Gubal Library. Its autoattacks don't just hurt the tank, but it constantly hits random party members. That alone makes healing in that boss so much more fun because there is actual danger in leaving your teammates at low health and waiting for something to come off cooldown. I also like how it punishes failing mechanics not with a vuln up, but with a dispellable debuff (heavy/frostbite/slow). We barely ever use esuna and those debuffs are actually worth dispelling.
The next boss i think is also very well done is Odin from Urth's Fount. Most of its mechanics are random, and a lot of the damage it does is proportional to max hp, which means you cannot outgear it too heavily, and being undergeared isnt too punishing either. i think its tuned at the perfect difficulty between normal and extreme content, and i really wish we had more fights that scratched that hard-but-low-stakes itch (not in dungeons, but elsewhere). Its overall a really good fight.
Finally Nael from ucob is probably one of the best designed bosses in the game imo. All of her mechanics happen in a timeline, as youd expect from a ffxiv encounter, but at the same time all of its mechanics resolve randomly, on different party members, in different order, etc. Nael is also good because while failing mechanics will most likely result in deaths and eventually a wipe, its not a forced wipe like in many savage encounters (e9s is particularly bad about this). Its mechanics flow like clockwork and you can recover a bad pull if you know what youre doing. Now, im not saying that dungeon bosses should be ucob-difficult, but nael does a good job of making every pull of the same fight feel different no matter how many times you do it. You will always resolve the same mechanics as everyone else (a lightning, a doom, 3 fire stacks) but the order and execution will change almost every time.
RNG mechanics keep fights feeling fresh, and dungeons that will be farmed for weeks need exactly that. A dungeon boss doesnt need to be overly complex, but dungeon bosses could use more random mechanics to keep them from being monotonous. Since nobody cares about parsing dungeons, RNG mechanics truly have a place to shine in dungeon bosses, and failing them doesnt need to be overly punishing either for them to be fun.
2. Identify a boss design that, in your opinion, fell painfully short of its potential. In what ways could it instead be made a fun fight?
The second boss from castrum abania is one thats well made. Or would be, if its mechanics were clearer. I really like how you have to see what element you have to attune yourself with, but it has one of the worst tells in that you have to read the chat log. I know the boss gets a buff on its status bar, but thats usually visible only after you probably already took damage from the reflect. Its completely unintuitive and the fight often devolves into the dps killing themselves while the tank inevitably dies to the tankbuster.
It has good ideas on principle, but just needs to be more intuitive so it doesnt go downhill so easily. Alternatively, its a bit too punishing. However it definitely had some good potential and an unique mechanic.
3. Identify a unique part of a dungeon's experience between boss fights--be that something related to its trash packs, a particular mob therein, its environmental mechanics, or even the way mobs approached during a certain time--that made that dungeon more novel and interesting. How could that be improved upon? Or, how could that be applied elsewhere (e.g., to a dungeon that instead lacked anything of note between its bosses)?
Im a fan of open rooms with trash packs, rather than actual hallways. This is better seen in Brayflox longstop, but its also present in aurum vale. the reason i think its better executed in brayflox is because for starters you actually can choose how to navigate that big room, and it very often differs between DF groups, while in AV you often just stick to the wall and pray nothing aggros you randomly. Rather than killing everything to open a door, you kill everything on your way to that door. it just feels more organic.
I also like environmental hazards like the exploding crystals in dzemael darkhold or the puddles in AV. makes tank positioning a bit more relevant without being overwhelming.
4. Finally, more miscellaneously, what are some concrete mechanics or interactions that you might like to see in future dungeons? Contextualize them.
Generally speaking i just wish there was more of two things in dungeons. 1. Random mechanics so the dungeon youll farm X times doesnt become stale, and 2. Proportional HP damage, so that you cant outgear or undergear it too hard.