Being a gunmower is satisfying! haha mowed so many my browser crashed the game with to much memory being used hahahaha. My feedback points are mostly being very critical - The buttons to play/settings weren't obvious to me in game, so I feel tweaking them to help with that - the idea is cool though. the update button on the main page Im not sure what it does, but you can just keep pressing it and it keeps appending. Ammo never mattered for me, so this is probably difficulty scaling or something to tweak (game jam time only allows so much). I was using bullets the whole time but ended with 25k bullets for example. Something that I think wouldve been simple to add depth is randomly making an alien red, and doubling their hp and damage so they are like a mini boss, or changing their move speed so some are randomly faster to give variability and intensity which i feel overtime diminished a lot. And an easy tweaked polish note is you can see the spawn point on the left side, if you just block it slightly it would give a little polish feel for very little effort. What is great about what you have done though, is you can easily expand it - new monsters, weapons, coop mode(?) etc. Awesome job! :D 
Viewing post in Last Weapon Stand Stand jam comments
Thank you for a thorough review, do you play on a wide screen? I noticed that the main menu buttons gets unaligned when when I connected to mine.
We had most of what you said as things to implement, different speeds and health on mobs. Mini bosses where nothing we discussed but it's a really good idea! Lack of time made the game unbalanced.
Thanks for playing and good luck with your own submission that I will go try out as soon as I have the time!