Not a bad try for a first game, I hope future games will be much better.
At the title screen, I noticed there is "Info" and also "Help." The Info button tells how to play the game kind of while Help just gives a button saying "Soon" which is incredibly pointless. Could have just not added the Help button given it seems to serve no function whatsoever.
Starting from Level 2, I began to notice a few issues. When jumping on the cacti. you take damage for every second you are on the cacti. A couple of seconds of invincibility after losing a heart would help greatly. I also notice that if you are hugging a wall or platform wall, you lose the ability to jump until you move away from it.
I noticed the only levels with any kind of difficulty were levels 2 and 5. Level 2 for the cacti that take off way too many hearts at once for simply being on them for more than one frame. Level 5 because you kind of have to hope you land on the latter platforms fast enough that you can shoot the other cacti to avoid losing health. It IS possible to just lose a heart or two and just drop down to the door to finish the game if you have at least 3 hearts though.
The medals all worked, I got the level 1 medal after finishing the first level and The Nopal after completing all 5 levels.
The game lacks audio all around; no sound effects, no music, no noise at all. I hope the next game adds in some audio to keep players a little more interested when trying to complete the game.
Overall, not a bad first game but I got a feeling you have a lot of room for improving too.
EDIT: No, 1, 3, and 4 are fine on their own. I would focus on bug fixes before building more levels to be honest.