I quite enjoy the small details, like the parallax background scenery and subweapon effects. The music is nice too.
Sometimes when I destroy one of those stacked monsters on the bottom the top ones refuse to drop down and kind of just hang in the air. Your movement can feel too limited compared to that of the enemies which adds to the difficulty so just like in the old games.
Having to open the pause menu to see subweapon controls can be annoying, since they are somewhat arbitrary. I think button combos would work better with gamepad input, otherwise there are plenty of keys to map to on KB+M.
While the level design has amazing aesthetics, functionally the platforming can be confusing because of lack of clear separation between foreground and background. I mean thing like showing the player where they can stand on and not just part of the scenery. I understand this is tricky to do though.
Overall, it was a great experience. I liked it!