ahoy.
i had a nice playthrough. although i was unable to reach the boss, i think i made it more than halfway through the game and had a good time. as before, a warning that I suck at bullet hell/heaven/whatever games, so any criticisms should be read with that in mind.
starting off simple, the new UI and music selection are both very good. both fit the style of the game very well. one UI suggestion would be to add more notice about your currently equipped gun. right now it's just the border getting text, and while it's conveys the idea well and is visible from a distance, i'd still consider adding some highlight or something similar, since there are UI elements by default which have that text highlight effect.
i mentioned this last DD i'm sure, but the background of weaponboxes being an ammo counter + being the correct ammo color is a great design decision. usually these games have issues display this information to players, leading to frustrating moments of a player misjudging their current ammo and dying. i had no such issues there and was always aware of my current and remaining ammo.
the level design was good. there was a healthy mix of open rooms, caves, buildings of some sort and some inbetween mixes. there are also some QoL fixes i think were not present in DD. things like the ammo and guns going to the middle of the map on level completion. good stuff.
you mentioned being interested in the difficulty. while i don't think the game is very difficult, the issues is that it comes in waves. for example, the M(eteor ?) enemy came in later in comparison to other enemies, but the stationary orange alien that fires projectiles is much, much more dangerous. Same with the spawner enemy. Both Spawners and Meteors stand around a small area and patrol/idle I come closer, while the orange projectile guy shoots me from offscreen. If there's a lot of them, my screen fills up with red projectiles incredibly quickly. The most dangerous of all is the moving projectile enemy, and he would be my #1 priority by far. Levels with caves then became piss easy, since i'd sit in a corner and shoot the melee enemies, then mop up the projectile enemies. Compare that to a fully open level where I need to dash and move around constantly. I think this is the design of games of this genre and is to be expected, but perhaps some balancing is in order. Maybe prevent the stationary aliens from shooting from so far away or something.
again, this might be an issue for me since i suck at these, so i wouldn't worry too much about balance
my favorite part of the playthrough was making fun weapon combinations. i had a cold damage (Northern) SMG, and a modified triple shotgun as my top loadout. it was great fun mixing and matching weapons. perhaps a good levelup choice would be holding more weapons.
a small error i noticed was being able to use mousehwheel on the map select screen. i thought it would move the map up/down, but instead i was able to switch guns there. not a big deal, but it's always a bit immersionbreaking to be able to control my character on the map screen.
the game was lots of fun. as always, keep up the good work