This game is BRUTAL.
Full-level progression reset and the health staying with you between levels really makes it HARD. I also felt like some of the colliders with the enemies, spikes, and saw blades were a little too big. For example, in the second level where you have to jump right between those two spike beds, I have yet to be able to do that after like 10 tries.
Also, the Skeletons inconsistently moving, BRUTAL.
Did beat it though. 4th level was my favorite (felt like a stealth game), 5th was also pretty solid, 1st felt the most like a classic platformer, level 2 was also pretty good, and level 3 I did not enjoy.
Good game!