I liked this a lot! It is classic snake, but executed really well with a few twists. I think chaning the environment every 10 coints was great touch. It made me have a real sense of progression, and it kept the game interesting at the same time. I also liked how the game looked and sounded! The music was fitting and did not become annoying either. All-in-all a really nice experience. :D
My main point of feedback is that it is a bit slow in the beginning, but I guess this is a normal thing in snake. In the beginning there is not yet much challenge, because I move very slow, the level is not too complicated, and the dragon is still very short. I really enjoyed the later levels, when you have to think about where to move, and make sure your own body is not in the way. However, in the beginning these challenges are not yet there. Perhaps there could be a checkpoint system or something?
I was also wondering, does the dragon go faster as you get to later levels? I feel like when the dragon came out of the portal it got faster and faster, but when I pressed spacebar and released it again, the dragon returned to its normal speed. Maybe this is a bug? (I am not sure, haha)
This was a really solid entry! Great job! Especially if this is your first published game, then I think this is really promising! I hope you will participate in more game jams in the future ^_^