The Vermin Druid relies too heavily on luck for his powers to be effective, and that made it next to useless in my games.
While the War Machine, on the other hand, could almost single-handedly slay everything in the rooms. It makes sense, in a way, but relying so much less on chance makes it OP in the hands of a tactically minded player.
The Maid is great for support, but a bit weaker on her own, though it makes sense with her theme.
The Sorcerer's Research feature should be addressed in the rules to clarify it can be used before the first encounter as well, prompting characters to better investigate what waits for them and take full advantage of it. It would be interesting if it applied to Chain Lightning as well.
If I get the chance to play it again, I'll give some more feedback.