Finally beat the game and got the good ending. I think there are 4 endings in total, not counting bad ends, but it's entirely possible I missed some. There are surprisingly few bad ends, I think only 3?
Thinking about it and it's entirely likely that some of the brainwashing choices could have lead to their own specific endings, but I just didn't try them out (clearing the game multiple times takes awhile).
I appreciate that none of the character quests or secret areas are necessary for beating the game, but if you want the good ending you Need to do the secret areas. Depending on how you handle the character stories and which walls you blow up, you can probably skip the Oz Sanctuary and just go to the Lo Temple.
My primary complaint for the game is how obscure a lot of things are. I have no idea how you're supposed to figure out some of these secrets without just wandering around the map endlessly peeking behind every tree and walking into every bookcase. I'm sure I'm not the only one who felt completely lost at times when trying to progress specific character stories or looking for a path to unlock a dungeon section.
Otherwise I really enjoyed the exploration and sex content in the game. There are a lot of really good, fucked up sex scenes in the game. I don't believe you can see all of them in the gallery either, such as the brainwashing scene on floor 2 where you go insane and rape the other prisoner. A lot of things only happen if you fail or get caught in traps (Stuck in wall sex, futa transformation, petrification, etc.), most other scenes are related to specific jobs, and everything else is linked to character stories.
If I had to give any advice, it's to press M while in the dungeon.