I like these criticisms.
I feel you on the backgrounds. I tried multiple but even now I couldn't make them really great. Now I totally get why games like Celeste and Hollow Knight use a spotlight.
I also realized in the last hour that some surfaces that looked solid were actually not at all. In one of the rooms there's a series of fans pushing you left and up into the ceiling. In a previous version there were a bunch of solid-looking non solid tiles so you would get stuck in each 'notch'.
Save points are so silly. At first they would trigger whenever the joystick was at all pointed up in the y-axis so as you walked by one you would trigger it unintentionally. Now there's a chance they don't trigger, probably because in the code it only checks on the first frame in which you input 'up' that the controller is not in a deadzone, instead of using a separate variable and ditching the 'first frame' thing.
I was a little bit worried about the clutter in rooms. Very sorry you and others had to deal with all that.
But I am glad you seemed to like it more than you didn't. Thanks for the pointers.