I loved it. It was simple and did not look like much from the images, but there was a lot! The music was awesome. The Yellow and Green areas were my favorite tunes. Is Earl a pop tart?
The controls were great. Idk if you meant to add it, but the mini-second of footing when you walk off a ledge that lets you jump is *chefs kiss* beautiful for platformers. The double jump was great! Not too fast of a fall speed, and every jump felt right. Nothing was out of reach or bullshit in terms of platforming.
The art was meh, but who cares? Not a lot of people can make a game in a month, and you made a functioning game with upgrades and music! I'm really glad with this game and the traversial and progression.
Simple? yeah. Bad? No. Great job!