Monks are a very polarizing class in 5e due to the chi system and subclasses, but that doesn't mean they aren't well built.
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Possibly one of the most exotic classes for a novice is the monk. Monks are unique compared to the spell throwers and sword wielders of old. They fight with their bare hands and martial arts-like skills, with plenty of subclasses to choose from. Still, some are better than others.
10/10 Four Elements
Unfortunately, one of Monk's coolest premises, which is essentially Avatar, is also one of the most underwhelming subgenres in 5e. While Monk has access to tons of new features, Monk's biggest problem is its ugly mind. The expensive chassis is the ki system.
All class traits that focus on "bending" consume a lot of chi, which means that most monks will run out of gas too quickly to take advantage of their traits. While the effects themselves aren't bad, the fact that they are tied to a very limited chi resource makes them mediocre compared to spell slots.
9/10 Sun Soul
Sun Soul is another example of the Monk, it has a cool concept of extending the attack capabilities of the Monk, but is limited by the Ki chassis. Also, the effect itself is too weak, approaching the Warrior's Arcane Archer subclass in terms of overwhelming impact.
Searing Arc Strike is a solid attack, but again, the expensive chi consumption means it depletes quickly. The Radian Sunburst is an inferior fireball, while the Sun Shield basically turns the Monk into a walking lamp. This is the final function of the class and it is very disappointing. For this alone, many people don't like the characteristics of Soul of the Sun.
8/10 Ascendant Dragon
It's time to revisit the "chi system is inherently flawed" topic, as it's a consistent failure in game design. Thang Long suffers from the same problems as the Four Elements and Sun Soul. That being said, Thang Long does have some benefits over those two.
Draconic Disciple offers ways to disable opponents with the Fear debuff or bypass exploits and resistances with Draconic Strike. Breath of the Dargon is a powerful AoE attack associated with martial arts dice. The appearance of the Wyrm and its upgrades really make players Feel like a mighty dragonborn. Unfortunately, they're still limited to small ki pools, so aren't a great subclass for Marvel's Iron Fist builders.
7/10 Drunken Master
Drunken Master is a great subclass, although a bit too specialized in crowd control. The Drunken Technique allows the Monk to bake the benefit of disengagement after triggering Flurry of Blows, avoiding any and all attacks of opportunity while increasing speed. Tipsy Sway allows for quick recovery from being knocked down and, more importantly, redirecting melee attacks.
Drunkard's Luck negates any disadvantage, while Intoxicated Frenzy amplifies Flurry of Blows to ridiculous levels. It's a very powerful style when used correctly, but tends to struggle against single, tough enemies. Having said that, if there's any martial artist who can come out of a random bar fight unscathed, it's Drunken Fist.
6/10 Long Death
Drunken Master avoids death by obfuscating fu, Long Death pretty much just says "no" to it. Death Touch causes the Death Priest to drain health from fallen enemies. The hour of reaping allows to intimidate a creature on one's Wisdom saving throw. Their livelihood, Mastery of Death, is by far the most impressive.
This feature allows Long Death Monk lives up to its name, allowing monks to spend ki points to prevent death without requiring ki. This means that Long Death Monks will persist as long as they are gassed, which is easy since they don't have the class trait ki uses. Also, with Tasha's rework, perks like Fey Touched work incredible with them.
5/10 Astral Self
Astral Self is a subgenre that employs one of the most iconic imagery associated with monks, the many spiritual arms that wrap around their backs. In classic Buddhist and Hindu art and Doctor Strange: The Multiverse of Madness, this looks and feels as cool as one would expect.
Arms of the Astral Self summons two additional arms for the player, using Wisdom instead of Strength when making Strength-related checks. Wisdom also replaces attack modifiers and damage rolls. They also extend unarmed strikes by 5 feet and change the damage type to force. With an affordable 1 ki point weapon, the Astral Self is a solid Monk class.
Ninja is one of the most iconic professions for fantasy martial artists, so this would be an oversight 5e has no subclasses of them. Shadow Way is a typical ninja build and the ki consumed is actually quite effective. Gaining spells like darkness, darkvision, invisible passage, and silence is incredible for stealth martial arts builds.
Shadow Step allows free use of the improved Misty Step in low light or darkness and gives an advantage on the first melee attack. The shadow cloak allows invisibility as one action under the same lighting conditions previously encountered. Note how ki is only spent on Shadow Arts, the rest of the features are provided for free. That alone boosts the class.
For those who just want to be a whirlwind of fists and steel, the Kensei Monk is the perfect subclass. The path of Kensei allows monks to become very good with their preferred weapons. Dexterity parry increases AC, while unarmed attacks in combat (which is pretty much always the case for monks) and Kensei's shots, increase ranged damage.
One with the Blade and Sharpen the Blade are basically more damage, plus the benefit of magic. Unmistakable Accuracy allows the Monk to re-roll once free. While the Kensei doesn't make waves flavor-wise, from a combat standpoint, there's no denying its simple effectiveness.
Ways of Mercy is one of the most flavorful and mechanically versatile subclasses available to Monks. They are masters of life and death, supporting allies in battle while sending death to those who cannot help. Their proficiency in medicine and clairvoyance gives them some great use outside of combat.
Hands of Harm turns combos into healing combos, restoring health equal to the damage they would have dealt. In contrast, Hands of Harm deals additional necrotic damage. Physician's Touch can heal physical debuffs during Flurry or poison enemies with Hands of Harm. The Hand of Healing is free after level 11, and the Hand of Ultimate Mercy can revive any creature that dies within 24 hours, provided a corpse is present.
1/10 Open Hand
Without a doubt the most classic and reliable subgenre of Monk, Open Hand is pretty much what people imagine when they think of Monk. The open hand technique enhances combos by knocking back, knocking down, or preventing enemies from reacting during the round. The integrity of the body provides quick healing when needed. Serenity grants the Sanctuary buff until the next long rest begins or ends earlier as usual.
Then there's the key to an entire subclass of Tier 4, the Quivering Palm. With only 3 ki points, any creature hit by an unarmed attack must make a Constitution saving throw. If they fail, their health is instantly reduced to 0. If they succeed, they still take 10d10 necrotic damage. Basically, the player can say "you're dead" like Kenshiro in Fist of the North Star.