I played the game for a bit and it seems fun, but I'm slightly concerned about how you handle the demo vs full version...
Is the free version just the full version with a 3 minute timer?
Since it's written in Javascript and it's not obfuscated, it's actually really easy to disable the timer inside the browser, so just in case you didn't know; I just wanted to make you aware.
I think if I was in your position, I'd remove the timer, but remove some features for the demo version. Though I've never tried selling a game (yet), so feel free to ignore me, but I think that if someone finds them self playing the demo for half an hour or longer, they're probably more likely to buy the full game...
the 3 minute limit seems a bit counter productive. It seems like the kind of game that you might actually hit a nice flow state.
One more thing about the demo vs full version... Have you looked into wrapping the game into an Electron app?
I'm not sure how complicated that would be since I'm not really much of a Javascript programmer.
Sometimes *.html games require setting up a local server if it requires any external calls (like loading assets), so I'm worried that some might see the *.html download and think it's going to be a bother.
Apart from all that, I did notice a glitch where if you start the game, then abandon it; the players gun is now on the title screen.
There also seems to be a Y Axis offset issue with some monsters...
I noticed when I killed some monsters, their dying animation showed off MUCH longer legs than what I could see when they were on the ground.
If I was to change anything (apart from what was mentioned above), I think music would really add to the experience... I think I'd compose a few tracks and let them fade in and out between waves, probably keeping the ambience for the bits in-between.
I'd also play around with the user interface a bit... it's a bit cluttered and I think I saw some text overlap when interacting with the loot crates.
Lastly; I'd avoid the AI artwork for the thumbnail... it's unfortunate that people assume that if a thumbnail is AI generated, everything will be low effort, but I do think the game has a fun style to it, so I don't think it would be too hard to come up with a fun thumbnail that better represents the game.
Sorry for being long-winded and especially if I'm coming across as over critical, I really am trying to be helpful.
I think there's something fun in your game and I hope it goes well. :)