I have never played Midnight but I have been a huge fan of the setting since second edition. And I think that Edge Studio did a commendable job bringing the world to 5th edition.

PROs

1. While largely a re-skin of the lore found in previous editions, the artwork and layout are really nice; easily my favorite of all of the editions
2. The rules updates to 5th edition are sparse but really elegant. I think that Edge nailed the Heroic Paths. While fewer than previous editions, each one is distinct, makes use of unique and quite underused 5e mechanics (e.g. Inspiration; Healer's Kits; exhaustion) and there are no niche paths. Each one is viable for any adventure. And since the paths are in reality level gated hierarchical feats, it makes it really easy to add these mechanics to something like D&D Beyond or other VTT services. These heroic paths work very well with any class/subclass combination making for some truly unique builds.
3. How they introduce encounters by creature type to the setting without having the reader to remember dozens of stat blocks was smart. And the stat blocks that they did include were well done (especially the night kings :) )

There are a few nitpicks that I wanted to bring up which I'm pretty sure can just be fixed with some simple homebrewing.

CONs

1. As said, the book is largely a re-skin of the lore found in earlier editions. The rules that are found inside clearly are aimed at attracting new players to this great setting without innundating them with a bunch of new rules. Which is fine. 5th edition already has plenty of rules and mechanics and races and classes and as I said earlier, I appreciate them instead of throwing new races and classes on the pile, they repurposed existing races/classes and took existing but underused mechanics and spruced them up. But I feel that they missed an oppurtunity to modify some existing rules to fit the setting. Something like stricter resting mechanics I feel would have gone a long way in bringing out the harshness of Aryth.
2. Another missed opportunity, is how important crafting was in 2nd edition. Since Legacy of Darkness did not change how the economy (or lack thereof) works, crafting should still be a focus. But crafting mechanics in 5th edition are TERRIBLE so I could have seen why Edge left it out of the book but I really feel that they should have probably made their own.
3. While power nexuses and black mirrors are covered, Covenant items are gone :( I can kind of see why. Covenant Items I would imagine kill any semblance of looting once you finally got one since the item would level up with you. Still, I thought they were neat...
4. In addition to heroic path feats, Legacy of Darkness introduces new (regular) feats and spells that are thematic to the setting. These additional feats are fine but since Heroic Paths also take up feats and the paths are all worth taking, I would imagine that none of the additional feats would ever be taken. I would probably house rule that everyone would get an addtional feat at second level or something so that they would be able to take one of these additional feats.
5. The astirax magic detection is pretty jank. Midnight and 5e in general introduce many different types of innate casters, full casters, and half casters, and quarter casters. There's also magical item detection that is discussed in the book but is left out of the Astirax stat block. I think that the mechanics could use a redo. As they stand, they don't really work.
6. While the lore is super rich and well written, it would have been nice to include some story hooks or like a short sample adventure at the end.

As I said, I have never played yet, but just reading through the setting, coming up with character builds and just letting my imagination run wild has been a total blast. Highly recommended for new players to sink their teeth into the Midnight setting.