Thanks for the detailed feedback! You have a lot of good points so If I don't address everything it's because I agree with you and I'm already working on improving it.
I'll make it so it's playable with keyboard only soon. Some of the skills can stack but it's not really communicated right now as I'm not sure if they should stack or just not be offered. The one you picked does stack so you would be doing +100 if you pick it twice. ? rooms are bonus rooms, where you can find treasure, some of which comes at a cost. I'll make them explain exactly what happens after you pick something.
Some enemies are easier than others and there are some that tend to annoy players. I think there has to be some unpredictability to make it so you can't just blitz through the game without using any skills/items if you're really good at tetris but I'll see if I can make some of them a bit less annoying.
The endless mode is supposed to be actually endless, did it not spawn a boss room on the first floor? I don't think I've seen that happen before