Thank you very much for the feedback, I will solve the mistakes you found and I will take into account each recommendation, I will answer you for each item below:
"1. At first I didn't know what the jump button actually represented. An icon on the button may help.
2. When your rat dies the control icons opacity has an odd interaction with the tilesprites."
A brief message about the controls could also help me, I'll see which one looks more cool.
"3. On the First level you don't actually have to enter the tunnel to go onto the next level."
Outch, I have to solve that.
"4. The jump on the 2nd screen can feel a bit finicky because the hit boxes are so tight. That may be fine, because it does set expectations for difficulty."
You're right I did it to increase the difficulty.
"5. I completely missed the 2nd mouse the first time through because I didn't know he was there.
On that note his text goes away a little too quick.
I would leave the informational mouses around like sign posts so that when you are next to them the text appears and maybe stays, and when you move away from them then the text goes away."
Yes, also weigh in that, for loafers leave it like that, point to improve.
"6. Dying is painful having to start over from the beginning can be frustrating. Which may fine, depending on what you intend. A checkpoint and life system may help, and after all of the lives are expended then start the player over from the beginning."
Good idea about lives. I'll keep it in mind.
"7. Overall the jumping feels good, and the movement feels good. I played it for about an hour, I'm not all that good of a player and kept dying."
Maybe the lives help in this. I passed a little with the difficulty haha.