I couldn't figure out how to hit enemies without them hitting me at least once as well. So effectively I never got past 4 kills and couldn't play as Marty, unfortunately. I may need to spend a bit more time on this.
One thing I found a bit tedious was that there was seemingly no way to restart the game when Andy dies, so I had to forcibly close the game and restart it.
Overall looks very nice, but I sure wish I could've progressed a bit further.