I think the author made movement like that just so that physics remains as realistic as possible. However, it is a bit too slippery I think for such small maps and precise jumping requirements and it would work better for a game like Sonic. Had this been finished with walking physics at least similar to SMB1 (where it's far more responsive) it would probably have a reasonable difficulty level. Right now, if you barely tap the directional keys you don't even move at all and if you hold down the key for a while longer you can't stop fast enough.
It's a great game so far in general and if it was easier and I could notice a lot of more rooms, I could have made a news.