Okay, more detailed thoughts on the base class:
Level 1: Martial arts, unarmored defence, weapon mastery. Martial arts die goes up by one, apparently to keep up with weapon mastery. This does not let it keep up with weapon mastery. Also give the monk's unarmed attack a weapon mastery feature, because otherwise it becomes a significant disadvantage compared to other melee attacks (plus Warrior of Open Hand is severely disadvantaged; more on that later). Unarmoured defence and martial arts are unchanged.
Okay, just let monks use discipline points from level 1, and let them add their wisdom modifier to their di points pool. This is the defining feature of monks and making them wait is akin to making full casters wait until level 2 to cast spells, and then only giving them two spells. Just give monks di points and step of the wind at level 1.
Level 2: Martial discipline (see above), unarmored movement. See above. Adding disengage to step of the wind is great and actually makes it worth spending a di on.
Level 3: Deflect Missiles improvement. A tiny bit better, depending on what you just deflected? Still situational but fun when you can use it. The counterattack feature might actually be worthwhile more frequently.
Level 5: Stunning Strike reduced to one attempt per turn. I think most of us agree with this, but why not give a SECOND option for spending di to go with it, so there is more choice? Most folks spammed Stunning Strike because they had nothing better to do.
Level 6: Empowered Strikes letting unarmored attacks do force damage. So...hmmm. This is a probably a wash, since very few creatures resist magical b/p/s attacks (swarms and demi-liches?), but a similarly few things resist force damage. Definitely makes the monk more effective against demi-liches!
Level 7: Heightened metabolism - so after 7 levels monks go from famine to feast as far as di points go. Just give them more di points to start with and give them something fun here, instead. Like stillness of mind, but make it a bonus action..oh wait, that's now wrapped up with purity of body at level 10 and called "self-restoration."
Level 10: Self-restoration. So this is kind of lame. Disease is no longer a thing, okay, but instead of being immune to poison damage you now can use a bonus action to remove the poisoned condition - that's a huge nerf against some fairly common opponents. On the other hand, being able to remove charm or frightened as a bonus action rather than an action is an improvement, but you have to wait until level 10 to get it. Overall this is at best a wash, but it feels like a nerf. It'll sure feel like a nerf when you are fighting anything that does poison damage!
Level 13: Deflect Energy instead of Tongue of the Sun and Moon. Why not both? Deflect Energy is a modest upgrade, since it will only affect targeted spells, and it's not like Tongue of Sun and Moon was that great in most campaigns.
Level 15: Perfect Discipline: again an ability that seeks to address the fundamental flaw with monks, resource scarcity, but does it at a level where that is much less of an issue. Just fix the fundamental problem at level 1, FFS!
Level 18: Superior Defence: So it costs 1 di less than Empty Body, but you no longer get to be invisible, which feels like a nerf. And you lose the ability to cast astral projection, which was very situational but cool.
Level 20: Defy Death: similar to Mastery of Death, which Way of the Long Death monks get at level 11, except it costs 4 points (or more) instead of 1. This is a terrible capstone (and no capstone at all for Way of the Long Death monks; hello backwards compatibility).
So, overall, I'm super disappointed. The big problem with monks, particularly at low levels, is resource scarcity plus lack of options, and this is barely addressed. Your unarmed damage gets buffed by +1, but those attacks lose out on mastery. Other than that...a few tweaks and a terrible capstone to replace the previous terrible capstone. But step of the wind is improved so that it is no longer "cunning action but much worse."
