The concept of it is really nice and appealing. However, there are a few problems with it. First of all, the controls only work 70 percent of the time, meaning for about every 10 times the player jumps, the controls don't work 3 of those times. so I would fix that bug ASAP. Next there comes the problem of the character being teleported to the gap in between platforms or to the next gap without any warning, so yet another thing worth fixing. Now I come to the point of graphics... I understand that this is an ameteur game, so I can look past some aspects of this. Here's a good pointer for the graphics, starting with the background: You want to fool people into thinking that you AREN'T using one background, and the way to do that is to make one long background that you can loop without people noticing, and a good way to do that is to draw the background in a way that you can mirror flip horizontally and it looking somewhat different. With the platforms, may I recommend making at least 5 different platform sprites so that the game doesn't look graphically unpolished. And finally, i would make the character model smoother by adding in-between frames between the frames you already have with your character model. If need be, ask an animator to make a character model that is fitting for this game, and don't ask bigger animators, ask smaller animators who are looking for work. And finally, I would add sound effects (and for extra effect, edit them in Audacity [a free audio editing software] and give them a reverb to make it SOUND like you're in a cave.) Also I would maybe change the music to a more fast paced song that can loop really well (ex. being Megalovania from Undertale, it loops really well on itself.)
Anyways that's how I would improve it. Good luck!!