Apologies for the late feedback. Here it is:
Astonishing job!
The level of polish is amazing. It is a feat to get this level of polish even if the jam's time constraint wasn't in place.
First of all, of course what stands out is the visuals of the game. By itself, the artwork with the pixel art is already really good, but with the addition of the shaders you were able to give soo much more character to the game. It feels like I'm playing some modernized version of an arcade, really cool stuff.
I liked the funny vibe!
It's good to see that you were able to have very consistent mechanics created in this short time. Any time I lost the level it never felt like the game was cheating me out of a win or just bugged out, it was always my fault. This is always an important aspect of a game, but is an even bigger factor in a game like yours where the player only has a single input.
Really good work with the music.
The main thing that I felt was missing was more variance to the obstacles, specially of a more dynamic one, which could be one that moves, or has a different physics interaction with the player, like bouncing them off maybe.
The objective is also a bit unclear the moment you get into the level. Particularly because of the similarity to something like the Chrome Dino Game, that even you referenced, it initially seems that the only priority is to survive. Then it takes the whole level of taking it easy to realize you lost because you were not fast enough. So an indication of the objective or a tutorial at least on the first level would definitely be welcome.
I think you have an awesome base that is already good by itself, and if you wish to expand upon it can be even better. I'd recommend keeping the rock with just one input and working with what you can add to the level.
When it comes to your GDD, it is lacking depth in all fronts.
Remember that the GDD is not a task that has to be done before or after the development, it is an important first step of development itself. Other than being part of this jam's submission, the reason why it's important to create a solid GDD is because there is a lot of value during making a game to have a clear reference of goals, inspirations, what are you trying to achieve, mechanics and interactions.
Especially when in a team, it makes communication easier, reduces doubt, and makes for less reiterations needed.
It is not meant to be a presentation piece, but a source of truth for the developers, it's what should drive your decisions.
So especially if you plan on expanding the game from here on out, I'd invest some time into a more robust GDD. Detailing more of the type of ambience you are creating, the mechanics and how they interact with each other, visual references to the art. All of these will help you during development to have a clear mind of what you are trying to achieve.
This will not affect your game's chance to enter the top 10 games