MASSIVE SPOILERS
After 4 hours of excruciating pain, I somehow managed to clear this game.
About 80 outta 100 levels were OK. But all the problem is in the remaining 20 levels.
This game has a very complex physics. Your height of jump scales with your speed, you can bounce off the wall for extra speed&height, and the character feels kinda slippery and takes some time to stop entirely after running. Well, that's not a bad thing. The problem is, some of the levels require insane accuracy and tricks to proceed. And these kind of levels(48,37,28) are very unforgiving amount of time limits. Doing these tasks are extremely aggravating since your character moves quite fast and really hard to control precisely. The more you proceed, the worse it gets.
Please, do yourself a favor, and do not play this game. If you don't like gut-wrenching hard games, you won't enjoy this game at all. If you'd like to play fairly challenging platformer like SMB, go play SMB again. If you'd like to play insanely hard platformers and test your patience, go play some kaizo IWBTG fangames instead.
Also, the ending doesn't reward you at all. It just shows you two pixelated trees and the amount of deaths you had.
Half a star for a nicely-drawn old man from the beginning.