Edit: The game was updated and works now.
Actually, contrary to what I expected, it's not half bad!
If I forget the graphics which are pretty underwhelming, it's a quite diverse game with many varied sequences and surprising twists. I mean, if you revamped the graphics, even with some freely available art if needed (e.g. Kenney assets, people on OpenGameArt.org…), it could considerably improve the quality. Now there's a lot of "plain colour" rectangles and overlapping tiles creating stairs – it's simply a bit messy.
Another thing you might want to reconsider is the first few moments of the game. You have one shot at a first impression, and you choose to waste it on pretending the game doesn't work. And it takes quite a long time until the game tells you otherwise.
The problem with this is that a newcomer might just take it at face value and close the game. You also can't move forward until you click on the "1 player" text, which is counter-intuitive. I just thought the game *is* broken because the player seemed stuck.
Since "1 player" is the only option and the first scene might put players off your game before it even starts, I'd remove it.
Imagine a really cool movie starting with a minute-long shot with a plain white screen. No audio. People would look around nervously, tell the cinema manager it's broken. Then the movie would say, “Oh, the movie broke. Let me fix it.” – and then it would start. No, such a scene would end on the cutting room floor almost instantly.
You can mess with the players for sure, but the players have to know it's intentional all the way through… which is not the case here. And doing this when the players aren't even invested in the game yet is the worst possible time.
The rest of the game is pretty good. You probably should be able to close the shop window by clicking on the shop icon again (not just via Escape). While we're at it, dark blue text on a dark green background isn't exactly easily readable. The jumping physics was sometimes weird, which was most noticeable when climbing "stairs" during the bridge sequence – you bounce a lot. And the spaceship boss probably has too much health – he's not hard (he shoots the same pattern of easily-avoidable missiles at regular intervals), but he takes a long time to destroy.
It's a flawed little gem. I was honestly surprised at the amount of content and various levels this game throws at you, but for plenty of reasons, it's far from perfect in its current state.