its alright for beta, however theres one glaring problem tho, lack of knowing what to do, I got stuck on the first level(or the second if the pre-level counted I was left confused for 30 minutes trying to figure out how to get pass the black wall blocking the exit and last light flower? (honestly I don't know what they are called) also I would recommand to lower to effect sounds like when you get hurt, its way louder than the music and its distracting, also would be nice if you specified that the black blocks deal harm to you, enemies are kind of obvious but blocks aren't, also not sure if this was intended if you are jumping in darkness your "sanity" meter is dropping slower but when you are jumping in light its charging faster? its just something I find odd since I presume it wasn't intentional since if you stay still the "sanity" meter charges slower and drops quicke, also random ability to clip thru random walls, like the part with moving platform where it has a hole in the ground you can jump in to move around, just walk towards the left and you go into the wall, it doesn't do anything so I suppose its a glitch aswell?
beside that the main thing this game is platforming, which it does pretty well, you are moving at decently fast pace with good enough jump so the gameplay isn't frustraiting, the music playing in the background is very nice indeed its enjoyable and nice but can be distrubted by the "hurt" noise, also can you tell the player "find the key" when they get to the door down under since "press "e" to open" is missleading and I died couple of times thinking I was doing something wrong before releasing I needed to find a key to open, aside from that I would recommand being able to refil your sanity meter faster or have more light around or make the sanity meter drop slower, and make it so you the "monsters" you see around are a bit more aggresive, more speed will help, also make the player flinch when taking damage to make them aware that something is happening and not some random effect sound is playing, the level design is good, infact I like it, its simple and it doesn't feel empty, the concept of the game its going for is intresting and is fairly a nice idea and I like it.
overall, fun as a platformer, I like the concept the game is going for, the first level design is nice, I can't really judge much since this game is in beta but I hope for the full game some of the issues I noted are fixed beside that I hope you keep going and continue making games.