As everyone has mentioned already, this is very good for a first attempt at a level. There are no voids or grossly unfair enemy/save point positionings. However, I did find a misalignment that led to a wallswim, on x995 y1002, going right. I would like to offer you some tips for level construction, based on things in this level, though.
First, there's very little in the background in most places. For the most part, I feel uncomfortable playing a level where I am in a cave with no cave walls. Just floors and ceilings. A little more detail and creation of depth where appropriate goes a long way, believe me. Don't worry, though. My first attempt at a level was kind of like this too. If you spend the time to study the visuals and how they work, you will get the hang of it pretty quickly.
Second, some of the screen changes, from the caves to the laboratory and the Night City are jarring and do not blend together. In some cases, like if you are conveying space-warping, going through a doorway into a house, or making a dream sequence, this works, but if you are just moving from one screen to the next, these areas should blend together. If you want a good idea how that works, take a look at any given Nifflas level with multiple areas.
Third, the secret area really isn't much of a secret. I was expecting it to be a little more... how you say... hidden. Instead, you try to scare us off by saying it goes to the Void, which, once you get to know us better, you will realize is more of an attractant than a repellent. We simply love finding mistakes in other peoples' levels!
In addition, the secret area lacks substance. It's not enough just to find a hidden room. There needs to be something in that room that makes finding it worth the while. This could be a wide variety of elements, including an optional powerup, a key or warp to an alternate ending, a cut-scene, a blurb that breaks the fourth wall, a passageway that allows for fast-travel, a song that you can't hear anywhere else in the level, etc.
Fourth, there isn't a whole lot of ambiance in this level. In my opinion, if you are somewhere in a worldly setting, there needs to be some kind of ambiance happening. You do have some ambiance playing in some areas, but many others are eerily silent, with no reason behind it. Whether we notice as players or not, our ears will guide us almost as much as our eyes on whether or not we truly enjoy a level.
Still, you did good. I strongly suggest for your next level, should you choose to make one, to put an emphasis on the story. Doing that will set it apart from almost every other KS level ever made, even if it doesn't have any COs or custom music/graphics. I look forward to seeing what you do next.