Got to check this out with Theo, so thanks to them I got to try this in its full glory. Really really love the idea of a cooperative schmup, and the execution here was excellent!
The only improvement I think is warranted would be having each player's life/bomb count as separate. I think doing so would spare players from being punished in the event that their partner suffers lag or just makes a mistake, and also could lead to some fun clutch scenarios where one friend has to go it alone while the other eggs them on. And of course, being a cooperative experience, it's nicer to not get mad at eachother :)