I thought the game was pretty challenging on my 1st playthrough. On my second it was trivial. Somethings that need to change;

You should not be able to use the camera to scout through closed doors. Those bad guys inside should be able to jump me the second I open the door and I should be able to spy on them by panning the camera through the door. Same thing with secret rooms. It kinda defeats the purpose of a secret room when you can see the room through the wall.

You should not be able to gain advantage for having the high ground or by standing behind an enemy. Having free advantage all the time completely breaks the 5e rules set and makes stuff like Sneak Attack completely broken.

You should not be able to surprise almost every encounter by attacking them while they are in conversation with another character.

Starting the fight with 1 character while the other 3 hide in the shadows or in the rafters is REALLY cheesy and that tactic can be used on almost every encounter. You basically get a free opening attack with 3 out of 4 party members. I think its ok that this is a strategy, but enemies need a LOT more health so that your alpha strike does not remove half the enemies in the encounter before they get to act.