The core of the class is solid other than some stuff specific to the martial school rules. The archetypes are decent.
I'll have to do more analysis on the adept point system. At first glance, it's heavy on bonus action stuff, which is hindered by the bonus action to assume a stance. Also the need to concentrate on a stance is a bit iffy without support. Concentration can be broken by damage, the class doesn't have support for Constitution saving throws to help that out, and 2 of the 3 archetypes encourage a melee fighting style. There's a lot of abilities you can potentially never use just because you might not be able to keep concentration on them long enough to get an available bonus action. It almost requires Resilient: Constitution or multiclassing. Anecdotally, that's not an issue but those are technically optional rules.
After reading the specifics of the schools, I'd say the idea is ruined by a poor grasp of 5e mechanics when designing the actual maneuvers. IMO it loses the feel of the original martial adepts by going to a daily maneuver system instead of one that has a refresh mechanic. The whole thing would work a lot better if the resource mechanic was modeled after the Battle Master Fighter or Monk. The abilities are quite powerful in a vacuum, and the stance restriction and variable costs would balance that out if not for the bonus action needed to assume a stance and the "casting" times of the abilities clashing. Most of the bonus action school abilities are just trying to preserve the use of Extra Attack, which the Battle Master Fighter and Paladin do just fine with their maneuver mechanics and smite spells respectively. The Paladin does fine with bonus actions that add riders to the next attack because the Paladin doesn't have to concentrate on something else before being able to cast a smite spell.
It's playable but I wouldn't call it necessarily good. It ultimately reads like a Way of the Four Elements Monk with a long rest resource pool instead of a short rest resource pool, a counter-productive stance mechanic, and without the mobility a Monk would have to stay out of trouble.
