Finally got around to beating the Ringed City a few days ago. I really enjoyed Gael but as others pointed out Midir starts out as and impossibly daunting foe and then turns into a tedious grind to reduce his HP once you figure out his moveset.
Re: complaints about lack of closure and comparisons to DS2. I actually think that the series would be much more coherent as a duology, without DS2 (judging DS2 by what it is, not by the DS2 we never got due to the B-team and development problems). Both DS3 and DS2 explore similar ideas but DS3 shows whereas DS2 tells. The result is that DS2 not only is more clumsy in the way it delivers its ideas but it also cheapens and spoils DS3. A great example of this is the idea of cycles. In Dark Souls 3, the cyclical nature of the world is hinted at when we visit Untended Graves. The player finds themselves in a strange place until they realize that it is the Firelink Shrine from a different time, a different place where the fire faded until Ludleth willed himself lord. Afterwards Ludleth refers to both the player character and the firekeeper as "prisoners kept to link the fire", implying that we are stuck in one hell of a groundhog day. How does DS2 break the idea of the cycles to us? Well two or three characters tell us straight up that "countless kingdoms have fallen and risen on this very spot" and of course, the entirety of Aldia's character and his long winded monologues that are so out of place in a Dark Souls game.
Don't get me wrong, I actually really liked Aldia's "there is no path" monologue, but once again 3 shows us the folly of light and dark and sets up a way to bypass the two and enter a new, uncertain age (through the death of fire or usurpation of fire endings, depending on your interpretation) without resorting to walls of text. Instead it shows the stagnation of order and the dying age of fire and effectively builds on the ideas from the first game, for instance by showing us the dying Demon race and how each time the fire is linked the world becomes more corrupt.
Characters in Dark Souls are best viewed as concepts or ideas they represent. Gael is DS3's "Aldia monologue" because he represents the absurdity and drive of man - he is a fairly minor character who takes up a daunting task which he knows full well will destroy or corrupt him ("And yet, we seek it, insatiably...such is our fate.") Patches is a representation of humanity in general: low, wretched, and greedy, yet somehow persevering through every hardship in its way. The despairing yet tenacious nature of men is shown in Rosaria's fingers, the pilgrims of Londor, and the Dragon worshipers, each attempting to be reborn into something more permanent, something that would allow them to transcend the cycles. Oceiros is obsession, Prince Lothric is resignation, the locust preachers are seduction to nihilism. While DS1 focused on Lords, in DS3 the lords/gods are dead, leaving only men and their follies.
Also I think that the painting burning/creation is a nice allegory for the development of the game. Miyazaki chose to kill the series at the 3rd game, thus "burning" the painting before the "rot" sets in and giving the series a dignified death as opposed to milking the franchise. Hopefully his new paintings are not going to be all console exclusives (haha, who am I kidding).
You're correct in the sense that DS2 actually has a different set of core themes than its predecessor, and would probably be better off ditching the DS1 connection completely; while DS3 is simply a regurgitation of DS1.
The reason you misinterpret DS2 is, ironically, that you're resolved to see it as part of the trilogy, and concerned with the same subject matter. It's not. Even the intro cinematics bear witness to this - 1 and 3 describe the history of the setting, and indeed, the cycle of light and dark; 2, on the other hand, is all about your character and his condition. The fact that DS2 characters talk about kingdoms rising and falling isn't because the game is interested in the cyclic metaphysics per se, but because it mirrors the affliction of hollowing, of losing one's memory and identity to the curse. As such, DS2 is about finding permanence and value in a world of constant aimless change.
On a similar note, the point of Aldia's monologues isn't to showcase the absurdity and drive of man, but rather to point out that the cycle renders all actions and pursuits meaningless. A beautiful lie, he calls it. Aldia would likely see Gael as a pitiful fool, but would approve of the Usurpation ending to DS3, as he's all for destroying the established order of the world.
In the end, these ideas sort of come together in that, for the DS2 hero, saving himself and breaking the curse is equivalent to taking responsibility for the world, becoming a true monarch, and leading towards some unknown future beyond the cycle.
The games also have a very different atmosphere, where DS3 is DS1 made more extreme, with a definite "end times" vibe and the state of the world truly and irrevocably fucked. Meanwhile, DS2 is nostalgic and dreamlike, with an almost gentle sense of irreparable loss. That's why you find Vendrick to be a hollowed husk, rather than a mighty badass ala Pontiff Sulyvahn or Yhorm.
Needless to say, I generally disagree that DS3 builds on DS1 in any real way; rather, it repeats the same ideas in a different coat of paint. There are some ideas in there that could've been developed into something new, but they're overshadowed by all the mindless regurgitation.