I think it's a quite fun game, well done.
I like the art, the movement feels fluent, the jump distance and gravity feel just about right.
Yet overall, the game isn't terribly long – if you didn't always have to start from the very beginning, you could breeze through in two minutes. There aren't many game mechanics in play either, the danger consists solely of pits and spikes – although that is “sufficient” when the game is as long as it is.
I like the fluent transition when you walk between rooms; it looks great.
As for possible improvements:
– Sounds or music. If a game has neither, it usually feels a bit incomplete. Don't underestimate the effect a few chiptunes played when jumping or dying can have on the game's enjoyability.
– If you make the game any longer in the future, I'd seriously consider adding checkpoints. Repeating the same intro room for the 100th time just because you died to something seven rooms ahead will soon start to test your patience.
– You start the game by jumping into a pit which is an odd choice considering you spend the entire game avoiding falling into pits.
– I'm not a fan of the screen wipe after death; especially since it's top to bottom, so it takes an entire second until you're able to see where you're going after you respawn. I died way too many times by walking into the first pit while the screen wipe was still halfway through the screen.
– There are some tricks to make platformers more enjoyable, here I'd look specifically into the so-called “coyote-jumping”, i.e. be able to jump even a tiny bit after you leave the solid ground: https://youtu.be/vFsJIrm2btU?t=70
Here you have the opposite, and when I stand firmly on the very edge of a platform, I can no longer jump, which makes the controls seem unresponsive sometimes.
– You should probably prevent the player from walking back beyond the left screen edge. It can (and will) kill you off-screen.
– “You won” screen message is fine, but might seem a bit lazy. You completed the game; it's an achievement, so show the player something nice. Like the knight walking up the stairs out of the dungeon to broad daylight, finding a treasure, saving a princess… anything, really.
Here, you can still die even after you win because there is a spike on the side of the screen.
Don't get me wrong, I still think it's a pretty good game, but there are definitely a few ways to bring the quality up a notch without having to make major adjustments to the gameplay.