Prefacing this by saying that I'm by no means an expert on game design, balance, etc. Just from my personal experiences DMing for a Sword Saint character, theorycrafting, etc.
In the base class, I think every part of it is amazing and fairly balanced, with only the Spiritual Armor feature feeling a little underwhelming compared to other options available. I would love if the capstone feature was a bit more interesting, but being able to mix and match even more focus techniques is already insanely powerful and games rarely reach level 20, so I can't complain too much.
In the Paths of Devotion that come with the base class, there are a few features that define the subclass and make them interesting to me in their own ways.
1.) Way of Blue Metal is insanely versatile and it's ability to select focus techniques from other subclasses only makes it better with time as more subclasses are released. It's versatility makes it almost impossible to not be a viable option and you have so many ways to build the character. I don't believe it's broken in anyway, lacking the fighting style that other classes get as well as being a bit crit hungry to allow you to make effective use of all your options keeps it from going to crazy, especially with the lack of an extended critical range.
2.) Way of Musashi is, in theory, insane DPS with the ability to 'hack' your attack action, but that only lasts for as long as you have focus points to spend. With no built in focus point recovery like Way of Blue Metal, the Scatter Petals focus technique could quickly drain your focus points and leave you feeling as a somewhat worse fighter. In any fight you have the potential to go nova at any time, but you have to balance the desire to tear through an enemy's HP with wondering if there is maybe something even more threatening coming up next.
3.) Way of Rust is one I was insanely excited for, being a huge fan of the character the subclass is based on, but it ends up feeling a little empty to me. The roleplay side is built in, your character's life is essentially on the clock from the moment you take this class, which I love. However, the defining feature is the 'Body of Steel' feature at level 11, though I feel it's a bit late in level progression, and makes the subclass seem a little undesireable in my opinion.
4.) Way of Tadakatsu is the one I'm least confident on saying much about. It looks like an interested supporting/tank sword saint, but doesn't have any features that necessarily 'pop out' to me when compared to others.
5.) Way of the Ghost, another subclass that I don't feel confident on saying much about. Interesting, nothing seems overpowered or unnecessary, it fits what it's trying to emulate. I don't believe I have much to say beyond that.
6.) Way of Tomoe is another favorite of mine, being different from other Sword Saints in being designed for range. I wonderful archer subclass, though the focus techniques seem a little underwhelming. It doesn't quite have as much potential to go nova, since it's first major feature is seemingly all or nothing. Thunder Lotus has potential to add a ton of damage to a single attack, but if they make the save, they don't even take half damage, which can make the player feel like they wasted their focus points.
7.) Way of Yamato is the subclass that I have a strange love/hate relationship with. It's, in my opinion, definitely good, but I feel some of the features don't work well together. The main example of this is the Blue Crescent technique, which would seemingly work great with a Glaive, or similar reach weapon that does slashing damage, but then the dueling fighting style requiring using a weapon in one hand makes it hard to justify using a reach weapon. Other than that, I think it's super cool and am looking forward to playing it whenever I get a chance!
Overall, I think the Sword Saint is an amazing class that captures the exact feeling I love in tons of characters. Each subclass has interesting built-in roleplay that can help in deciding how a character would act and what their goals should, not to the extent that a Paladin's oath can, but it's something I love in classes.
I will hopefully review the other subclasses when I get the time.
A small edit: Realized something that for some reason or another, I just decided was impossible to do. I realize now that it's possible to combine both Blue Crescent and Wind Chain to make the former more effective when not wielding a reach weapon. I still feel like using 3 focus points is a bit much, especially at early levels, but it does solve some of my complaints about the Way of Yamato