Meanwhile I'm beginning to learn the hard way that the people who said the game peaked with the Ruined Tower were likely right (in the Dark Castle right now).
This was not quite accurate, the Dark Castle was just the nadir in terms of area design.
Overall I didn't mind it. It's true that many fights are easy, but I don't care about that and wouldn't want to play a tactical rpg where every fight is demanding. The Mind of the Master quest was pretty good though.
When it comes to 5e, I like short rests and its approach to Vancian casting where you get x number of casts per level and don't have to worry about the specific number of a specific spell. I have mixed feelings about concentration. I like the limit on buffs, but it seems pointless to cast them if sufficient damage can make them go away. A lot of these buffs are also rather disappointing; for a cleric, it seems far better to cast spirit guardians for free damage instead of one measly buff on one character. I like that Solasta includes an option to disable concentration but I imagine that works both ways.
Anyway, regardless of the flaws, I'm glad I decided to continue with it after playing 8 hours during the free weekend.