Greate piece of work, the menu, colors, graphics, LOGO and animations, music, great, so I'm gonna give feedback accordingly :)
1. oh if you use mouse already, make shooting with mouse not space! :)
2. mouseright-click has issues on web (I had the same problem with using Tab) (that could use spacebar )
3. Splitting seems too risky and uncontrollable to be practical, most users probably will use it very very rarely if at all. Some automatization or control over halves would be great.
4. Mouse cursor is invisible in this mess, it would be nice to make it stand out clearly. this is quite hard to achieve in these types of games, but would skyrocket the gameplay
5. Health cannot be numbers in action game, it has to be visual with clear color and shape so player can instinctively at once understand without thinking how much life is left, there is no time to stop an count your health points.
6. I have some weird lagging in LibreWolf Browser. Probably due to some effect being little too heavy.
Other than that its amazing game in general and three times more polished than what I managed to make :) Congratulations :)