Visuals
1 ... (main menu) -> too static add some kind of animation (easiest is probably camera movement based on user mouse)
2 ... (main menu) -> add GUI direct response (onMouseHover/onMouseClick)
3 ... (scene 1) -> aesthetics fits together +1 (1st scene, 2nd scene feels little off)
4 ... (scene 1) -> DJ is missing (after stepping down flaws starts to appear)
5 ... (game) -> outside is empty: I see Unity plane -> maybe something like image of env. in distance would remove this completely
6 ... (scene 2) -> feels rushed (if you compare scene 1 scene 2) & little doesn't fits best well
6.1 . (scene 2) -> massive decrease of motion (before dancing humans -> monsters)
6.2 . (scene 2) -> fells little of vs scene 1
6.3 . (scene 2) -> becomes laggy
Design
1 ... shaking camera would give so much weight into your game
2 ... do not lock player movement when talking pills (you take feeling of control out of player)
2.1 . make movement little more harder
2.2 . effect when changing ""dimensions"" is very good choice -> I love it
GamePlay
1 ... (scene 2) character get stucks by hitbox corners (are you using rectangle or capsule as base?)
Controls
1 ... movement good,
2 ... jump little delayed
2.1 . continue press of jump button works
3 ... stairs are bugged -> it feels like my character body extends by 80% in all directions
4 ... (scene 2) controls are off (hard to control)
Sound
1 ... (scene 1) ... fits theme very well
2 ... adding noise as footsteps would give a lot of weight
Bugs
1 ... (visual) -> characters walks/animates into walls
2 ... (visual) legs glitch into stage floor
3 ... (visual) flying humans