Needs better design
Difficulty is too low at the start, but suddenly ramps up to the point where it loses all skill elements and ends up playing up to luck instead, such as the level with just one block to jump on over a spike pit. It required a perfect jump to do, probably with only a frame or two of leeway.
People like their games challenging, but when it gets to the point of blind luck over skill, you're starting to go wrong.
Also, you ask any gamer; in very rare exceptions, no one likes to HAVE to die to progress. Many levels featured a drop over a spike pit with only one or two blocks below to catch them, and to land on them, you must have already known where they were, meaning more likely than not you'll die on the way down at least once.
Oh, and while I'm complaining, lower the speed of the game a little. It gets a little crazy in levels like The Fall. Couldn't tell if you did or not, but you might want to put a cap on falling speed to ensure it's not entirely trial and error.