Since you left amazing feedback on my game I will leave a ton on yours as well!
I don't have much talent for art in Unity and I started out with simple pixel art like yours (though yours is much better than what I could pull off). The biggest tip I can give you about your sprite art is to draw big. When you load up your game, look at how the sprites are blurred and fuzzy (except for the bullet, it looks a lot like on I have seen used in a lot of game dev courses). This is because you drew them small and did not upscale them in the actual drawing program. It is totally fine to draw in small resolutions like 16x16 but you need to resize them to higher resolutions like 256x256 to preserve detail. Unity does a poor job of upscaling on the fly (pretty sure the blur has to do with MSAA) so it often looks much better if you bring your assets to a higher resolution in the drawing program.
It definitely takes a lot of time and practice to get the hang of making decent enough looking art assets (honestly if this was your first try, I'm impressed). My recommendation is to find a friend who is an artist, find a good source of assets, learn how to use various filters and such like in programs like Gimp, Photoshop and paint.net to change random images from the internet into pretty good looking pixel art, and learn as much as you can about shaders and lighting. Shaders and lighting are your best friends, when properly used they can make a 4x4 sprite look awesome.
Learning as much as you can about visual design will help your games look awesome. Constant style is another big point I wanted to bring up. Basically, make the assets look like they were made by the same person, through editing or such like.
Ok, on to the gameplay. Overall, it is a solid platformer, movement is strong (you already know about the platform issues so I am not going to cover it), and has a good minimum viable product. However, there are a few key issues. First of all, there is a lack of enemy diversity. I assume it had more to do with the art side of things than the programming side, but at the very least the enemies should have different attack patterns. For example, maybe the blue ones can fly or something. You get the point. Spawning was an issues for me. I feel that I shouldn't have enemies spawning right next to me (trigger around spawnpoint maybe that stops spawn script when player is in a certain radius). Also, I didn't really like watching the enemies pop into existence, perhaps use a sprite to signify a spawn point or have them drop in from outside of the player view. I like the food idea that was good. The lack of a goal kinda hurt the experience for me. I felt like I should be going right to a endpoint but there was just another wall. Probably having the player start in the middle would set a more survival/exploration type mindset.
Ok, time for some wonderful resources to help you learn more about Unity. Be sure to check these people out as they will bring your code, art, sound and gameplay to a whole new level.
Brackeys - https://www.youtube.com/user/Brackeys
All around great dude. He has pretty good programming tutorials, but I mostly rely on him for the art and music aspects.
Quill - https://www.youtube.com/user/quill18creates
Want to bring your programming skills to another level? He's your dude. Seriously, he covers how to program a ton of different and difficult game types that foil many beginner Unity users (I should know. 4 attempts trying to make an RTS failed, then I found him. Got one done in 3 days).
Extra Credits - https://www.youtube.com/channel/UCCODtTcd5M1JavPCOr_Uydg
Watch them. They are awesome. Extra Credits is run by a bunch of insiders on the gaming industry, artists, animators, programmers ect. They also have a ton of different side shows like Extra History, Extra SciFi, and a couple others. The Extra Credits people are amazing. Gameplay is their thing. Just watch all of their videos. You will learn so much about what actually makes a game good and such like.
I just hit the word limit. Dang. That's crazy.