I really like the concept, and it does have some good potential. I really really wish that player 2 could attack with a different key like right shift for example, since Google Chrome kept constantly interrupting the game to bookmark the page. I think using control on a game that runs on browser is probably better to avoid. I also wish there was a bit more for player 1 to do, maybe something like a double jump or a dash ability to make movement more interesting for them, and to make the two players more distinct so it truly feels like a 2 player game, since currently you can easily play this on your own without even knowing it was meant for two players. Maybe allowing player two to move faster, but being harder to control their movement would help, making the game more interesting by requiring more coordination between the players and making it harder to play it with just one player.
Overall, I am pretty interested to see a new iteration of this game, cause I think it could end up being really fun! It's a really promising prototype and I can't wait to see more