I really like how dutchiez made his summary.
So here are my remarks. Without long justification. Contains no facts, just my opinion.
Agony:
Right now, I don’t see the point of the unavoidable agony being there.
There should always be a method to avoid agony, even if it puts a lot of extra work on the player to do so. In fact, I think to succeed in the highest levels it should be mandatory to use these extra methods. I would have loved to see more discussion on these. As far as I know, my suggestions (shield and bubble-device) are the only ones in this regard.
Agony resistance, on the other hand, should allow the non-hardcore players to reach these highest level later on—at a point where even higher levels are opened up for the hardcore players.
Difficulty:
I think the way it currently scales is fine. Mechanic changes to fights in higher levels are certainly welcome and maybe necessary to avoid the problem that the stat-scaling of enemies has a limit.
I would like to see more randomness added to the fights. I would be especially interested to see a fight were something random can happen while fighting (not in the lowest tier). At the moment, the only occurrence of such a thing I know of is the random transformation of Mossman. However, I have not noticed any difference in these but the visuals.
Additional Paths:
Variety (through randomness) and choice should be a goal of Fractals development. Not necessarily in the lowest tier, but starting from level 11. Variety should feel different (e.g., the two paths in Underground Facility feel different, while the paths in Urban Battlegrounds don’t).
This also includes different methods to solve encounters or optional methods to do some extra work to get a benefit.
Instabilities:
Really nice idea, but with very limited influence on play.
If it is possible to find a set of instabilities that do not aim at punishing certain builds, but instead at punishing unawareness, I would prefer one of them selected at random per Fractal. It should always be possible to circumvent the effects of instabilities by some additional effort (being aware).
If the current system stays, I think an achievement for doing all instabilities is a good way to go.
Rewards:
Good from my point of view.
I don’t think that pure gold is the way to go, especially not if it is only bound to the completion of the last Fractal (which encourages players to run through the Fractals).
Instead of increasing drop rates of ascended equipment and Fractal skins I would prefer if this just naturally happens through opening up higher levels.
I would like to be able to get/craft/buy something that allows me to get my guild people with low agony resistance into Fractals. My favourite idea so far is The Lost Witch’s Agony resistance banner. Agony resistance food (non accountbound) would be similar.
1-2-3-boss:
I think this is okay. A finetuning of what Fractal belongs to which category is helpful. I woul actually only exchange Aetherblade with Cliffside.
Lore:
I prefer the enigmatic Fractals. I think people should be given the opportunity to find out what is going on, instead of throwing the context at them. Interactable objects that give some short text seem to be a promising way.