Just finished playing this fun little game. First off, I just want to let you know that I did indeed complete all three endings. I almost didn't think of what the last one was, but it did eventually come to me. Actually, without spoiling it, I liked where you put it. If you're not paying attention, then you'll completely overlook it, but its placement makes sense. Nice level design choice. ;)
As for the aesthetics, they felt spot on. I love the color palette of the original Gameboy. Something about those greens just warm my heart, and they felt appropriate for this game. The design of the levels, enemies, and player character really screamed Gameboy to me, so good show on that.
My favorite part was the jetpacking. That whole part of the game just felt so natural and smooth, and I loved the part where you can see the outside just flying past as you jetpack to the next section. It was very visually appealing.
Now, I did find a couple of points of critique as well. They're nothing too major but would make the experience feel a little more polished if you ever decide to expand this idea out further.
First off, the camera felt a little janky. It would throw me off when it would suddenly switch positions. When you are using smooth scrolling, it's best to have the camera continue following the character. There are ways to make it more interesting than that, but it's very disorienting to have it suddenly change positions when you're used to it scrolling. The opposite approach would be to split the level into sections that the camera switches to as the player enters and exits said sections.
The other critique I have isn't a major one, just one that can easily be overlooked (I've made this same error myself many times). When you get the gun, you don't set any limits on how far the bullet can travel outside of the view area before getting destroyed. As such, all I had to do was spam the fire button, and I could clear out all of the enemies directly ahead of me before even seeing them appear on the screen. My recommendation would be to do a check on if the bullet has reached just outside of the viewing area, and if true, destroy the bullet. Other than that, I would say the game played appropriately.
Overall, this was a very good, short game. It checked all of the boxes for what makes a game a game, and it has the ability to be expanded if you decide you would like to do that. However, if you're happy with its current size, it works really well for a short game as well. Good job on this. I enjoyed playing it. Thanks for the experience! :)