I remember playing this quite a while back, never managed to finish it though. Now I'm a little less awful at platformers and the like, I wanted to try this game again, but it felt harder than I remembered it being. The first time, I actually got to a point where I had to sacrifice something, and this time I couldn't clear the second room after the first checkpoint, the one that tells you to jump after walking off ledges, no matter how much I tried. Even the very first jump took an embarrassing amount of tries. Double digits, easily.
I can see why, too. My jump height seems to be about a third less than it probably used to be? In the little preview gifs on this page and the bit of gameplay I watched from a video in the comments, the girl can jump a little higher than two full blocks - which means she can jump out of the pit from the first jump, and over the two plants near the end of the room below the first checkpoint. I barely make it halfway past the second block, which means that I had to reset every time I failed the first jump and taking damage from those last two plants seems inevitable. I can pick up the first heart, just barely. If I'm not perfectly centred below it, I won't reach high enough, but the top of the girl's head will just barely hit the heart if I am. Moving and falling speed also seems a little slower, though it's possible the gifs and video are just a little sped up.
Unless this is a difficulty tweak that got added in the newer versions of the game, could this be some kind of bug? I know holding the jump button for different lengths changes the jump height, but my jump is this short even if I hold it until I land on the floor again. With Z, with spacebar, even if I hold both at the same time. Not that I expected that to work, but it was worth a shot? And it's like this in both the web version and standalone v2.0.2 download. Sadly, I can't test older download versions because they stay stuck on the loading screen, even though I use Firefox.
Well, all of that only really matters if it is a bug. Please don't mind me if it's an intended difficulty tweak. I'm still not very good at platformers, after all.