I did saw gifs of your maps, i dont remember where, but on some srb2 servers you were in, and i kinda like that dark style it has.
Althought theres some issues here.
1- Map feels little bit empty, like, lifeless. You could try add some more decorations, based on the theme you picked, like some rocks or cliffs here and there, or some puddles of water, or even some more hazards or enemies, if so.
2- The crumbling at the start its WAY too high, maybe try lowering the FOF a bit, as the particles last what feels forever to dissapear, not even seeing what you have behind it, if not till 3 seconds later, the size also might affect performance when in netgames. I know that last thing because experience.
3- the death pit thats close to the floor, if you were trying to do a void, maybe try adding a black texture, as sky texture is usually for maps set on big heights, and also try to lower the floor a bit more, as its way too close to the safe ground, and one missclick could easily send people onto a safe death, if it werent for that.
4-On the same area as the previous point, you maybe could move the hole away a little further, or delete the whole floor thats its over it, as its a bit confusing ending on an empty room. Also try to make the hole bigger and more noticeable, as i took some time to realize that i was supposed to go down a hole on the ground.
5- Checkpoints, make sure you have them correctly numbered, from 0 as the first checkpoint, 1 as the second, and so on, up to 15 as max. So that way people wont respawn at the first checkpoint even if they already are half way on the map, and if possible, add the "Starpost Activator" linedef on the whole lenght of the room, if needed, try to remodel the room so you can add it as a single sector to activate the checkpoint, making sure to not miss even one.
6- Try using different textures whenever you do a parkour or whatever, on the platforms youre supposed to jump on, or even the walls, as the platforms might easily blend with the room, making them invisible unless closer inspection of the map, and that also applies in general for knowing where to go too, as you might not see the path correctly, if most of the walls and floors have the same textures. Try adding at least a visual hint of where to go, like different textures around the room.
In conclusion, its not bad, but it could use some rework, and more decoration to make it look less lifeless and empty, with some common issues that everyone pass through at some point, like rooms that blend with the hazards, and so on. You at least did a pretty decent try here, and thats what matters here, keep up improving!